We have a winner of SHERLOCK and DS2012! #dsxp

Depending on how you look at it.  A tip of the deerstalker goes to the fabulous — and fabulously named — Christine “CeeCee” Chappell!  Many fine answers, but this tops it for imagination and series-love.

Her entry…

Hi, Patrick!  You pose an interesting question, so I would like to take a stab at it.  If I were in charge of the Dark Shadows movie, this is what I would have done:
 Since Jonathan Frid was already so old at the time and probably not up to a big acting job, I would use him in the opening sequence of the movie, where we learn Barnabas’ history, including him as a grandfather or great-grandfather to the (Johnny Depp) Barnabas Collins we will be following.  He might have a line or two, a word of wisdom for his heir.  The main idea here is to let the audience know right off the bat (no pun intended) that we are acknowledging the history not only of the Barnabas Collins character, but also the history of the Dark Shadows show.  I think the audience would have really enjoyed seeing Jonathan Frid so early in the movie.  It would have given everyone hope that this film was going to honor the spirit of the original Dark Shadows.
 Of course, immediately after this opening sequence, the movie completely changes tone, and Burton is no longer honoring anything about the original show.  After this, he starts going for the laughs, so for the rest of the actors, (since we’re not re-writing the movie for this contest), I would basically use them for laughs, for fun.    
My natural inclination is to think that throwing in these original actors for short roles would be too disturbing to the narrative, would make the audience jump out of the storyline to say “Hey, look!  There’s so-and-so!”  For that reason, in general, it’s awkward to have cameos, but in this case, I think Burton is already having us jump out of the narrative so often anyway (mostly to say, “Hey, look!  It’s the 1970’s!”) that….so what?  Big deal.  If we have to be drawn out of the movie, let’s go ahead and enjoy it.
So next, I would have Katherine Leigh Scott reprising her role as Maggie, the waitress at the Collinsport Inn.  Of course Maggie is much older now, but she’s still doling out wisdom to her customers.  I see her now as a sort of “Flo, the Waitress” stereotype, chewing gum, calling everyone “Honey” and if we could get her into one of those 1960’s blonde beehive wigs (reminiscent of the wig she wore when we first met her way back in the opening weeks of the original Dark Shadows, only now the wig should be more dramatic, more exaggerated—like everything else in this movie), that would be great!  Once again Maggie the waitress has a brief scene where she warns newcomer Victoria Winters to beware of the goings-on in the “house on the hill.”  It would be a nice homage to the original show to replay this scene.
After this Lara Para makes an appearance as….the witch Angelique?  Perhaps.  In the 1970’s, any woman might expect a visit from “the Avon Lady,” and Lara Parker appears on the doorstep of Collinwood, touting beauty products to the mistress of the house. She doesn’t actually get in, but instead  I see a scene where Elizabeth (Michelle Pfieffer) answers the door and they have a brief exchange where it is mentioned that though we are still beautiful as “mature” women, none of us are as young as we used to be, and we could all use “a little help.”   This exchange, between two older actresses (who are actually aging quite nicely, I might add) would border on the “catty,” and written by someone much more talented than I, would hopefully end up being quite entertaining. 
As the large front doors of Collinwood are gracefully (or not so gracefully) slammed in the face of the “Avon Lady,” without her making a sale, she gives the evil eye to the potted plants on the doorstep, and they instantly wilt. 
Now, as for Christopher Lee, I actually kind of liked his performance in the movie.  I’m not really sure I would change that part, maybe just give him more to do.  But since it would be easy enough to put him in a costume and make-up for another role as well, if he would be willing to do it, I would like to see him in a brief appearance of the Caretaker in the Eagle Hill Cemetery.  There were plenty of opportunities to visit the cemetery, so why not have that Caretaker, with his gas lantern and quavering voice, warning not to disturb the dead? 
Finally, David Selby is also (perhaps) reprising his roles as Quentin, both a ghost and a werewolf.  He is the ghost of a werewolf, haunting the halls of Collinwood!  I see him sort of like that John Cleese ghost in the Harry Potter films, floating about and appearing at the most inopportune moments, making ridiculous comments on the actions of the live characters.  For the most part they ignore him, merely tolerate him.  But there could be a bit where he pays special attention to Carolyn, and that might help explain something about how and why she has become a werewolf.
Well, those are my ideas.  Each actor only gets a few minutes on screen, but I hope they would be a few minutes that would help reconnect the audience to the original Dark Shadows without noticeably changing the Seth Graham/Tim Burton screenplay (but only because you said we couldn’t do that for this contest, NOT because I wouldn’t WANT to change the screenplay).  Anyway, I would hope that these brief appearances would also showcase the talents of these wonderful actors and actresses.
 In the words of Dr. Praetorius, “You are wise in your generation.”
Fantastic answers.  The good news is that a sealed and minty-fresh, blu-ray copy of SHERLOCK, series 1 is soon on its way.  The bad news is that a sealed and minty-fresh, blu-ray copy DARK SHADOWS (2012) is soon on its way.  Haw!
My take on it is simpler.  And, because I’m not in the contest, I can tinker around with the script.  No one raves about seeing anyone in that film other than Greene, Depp, and Moretz.  Even Michelle only gets a golf clap.  No, the star of Dark Shadows is Dark Shadows… done correctly.
So, for me?  I’d have cast Selby as Roger (and he would not have abandoned David) and KLS as Elizabeth.  David Selby is never too old for anything.  Heck, I’d cast him as David.  Well, maybe that’s a bit extreme.  But use these people as your big guns.  YOLO, baby!
If I had to keep Moretz, whose presentation by Burton really gave me the creeps, I would have made her a granddaughter, opening up questions about the missing parents… to be answered in the sequel.  You gotta throw Ben Stokes into the flashback, and that’s your Christopher Lee.  If you let Barnabas (when chained) be Depp’s actual age, then Parker could have easily played Naomi.
That leaves Frid.
You know, you just can’t tell a basic Barnabas/Julia intro story without the cure aging him.  It’s part of the ritual, as James Whale would have said.  There’s your Jonathan Frid.  Playing the real Barnabas Collins, aged by the serum.  You know, with dialogue.  As much as he wanted to say.
Yes, I’m tinkering with the script.  But just a bit.  And while I’m at it, I would have intercut between the past and present constantly, like GODFATHER II.  That way, the 1795 Barnabas is seen losing Josette to Widow’s Hill just before the 1972 Barnabas reverses that fate.
But I like what you came up with more.