It would be nice to have one or more of the surviving classic Doctors in the special, but I don't think its a deal breaker. I've been a fan for close to 25 years and I'm willing to judge the special on what it is, not what I wanted it to be.
Yup. I'd love it if Peter Davison popped out of the Tardis with Smith and Tennant but I'm not going to hate it before I even see it just because he doesn't.
Yeah, I don't think anyone is talking about hating it before even seeing it, so that's a red herring. At least, I'm not. And, it may be a great story without any classic Doctors. However, I'd still hope for at least one to be included in some fashion. Not just a scarf or old clips.
In short, a great story with a classic Doctor would be even better than a great story without a classic Doctor because it IS
the 50th Anniversary.