I'm a Trek fan, even an active member in a Star Trek fanclub, but lately I haven't been interested in turning my room into a Trek shrine. A love to see a nice spaceship model, even have a Bat'Leth hanging on my wall, but my collectors hearth lies with LOTR.
It's not TOS but TNG that created an uprise in the fanclub & collecting business. And DS9 did well too. With the end of Voyager things started to get down, people losing interest. Enterprise was both loved and hated but I don't believe it attrackted many new fans. But the fans that excist aren't just the oldies/ TOS-fans either. I think most are in their 20's or 30's. At least the ones that do something with fandom except loving the episodes, I'm talking about meetings, conventions and collectibles. But from what I see it's not the size of the fandom, rather the interest. I don't see many fans putting down a couple of hundred for a figure. But I know a lot who would pay that kind of money for a spaceship model. That's the thing that lives among a lot of ST fans. I think an alien like a Borg or the Species 8472 from Voyager would do well too. Things that still leave some imagination. Action figures (like the 12") would be the thing, poseable and not too expensive. Like ArtAsylum did with extra bridgeparts of Enterprise, so you can create your own pose/ scene. Only then not bring out all except one.
The LOTR figures take me back into the movie, they suck me right into a scene. The Star Trek figures don't do that for me, I don't get the dynamic from the piece. Therefore I won't collect them.