When Kamen Rider 1 and 2 showed up in the Drive vs Ninningers special, it seemed pretty clear that they were re-built. I don't know about the other suits, but I assume they'd re-make those too. I would imagine the showa suits would be in pretty bad shape, and they can modernize them a bit (by making them easier to wear or something, I don't know, that was just conjecture).

Considering Toei has had to remake a lot of the past Sentai suits, it's probably safe to say Rider isn't much better.

People tell me that the original suit for Kamen Rider Black XR is still around in bad shape. Also is the Kuuga suit use in Decade, the same one used back in 2000 or brand new one?

Personally, I doubt they'd keep on to the original Kuuga suit from 2000, but they very well could have.

Considering Kuuga's low budget, I think they might have replaced the used models from the show for all his appearences after that. I don't think these things, especially the stunt suits stand the test of time very well in general, so I doubt that even the suits from the last few years are show-originals. I mean, Blade even had the main character suit replaced by a poorly repaired one in one of the first episodes (I guess the shiny material isn't very strong. Still his matte belly makes me shake my head very single time) so I doubt these things are made to endure more than one full show.
Also another good example regarding the Blade suits used is that the helmets use a different shade of Silver in the newer versions that has more of a golden touch to it. So if those younger suits have been replaced already, I don't think they'll use old Showa or Kuuga suits anymore.

I swear every time I see Blade in a crossover post Decade his helmet looks all muddy and brown.

It's not just now; when you see early Riders show up in later stuff in the 80s they were obviously in remade costumes. Rider 2, in particular, has a different costume almost every time he shows up during the Skyrider/Super-1/ZX era.

Yeah, their choice of paint wasn't the best :/

Kamen Rider has some serious continuity issues and they just hit me right this second. in Decade they treated each Rider season like it's own separate world. If that's true.. how the heck do team-ups work? Or Taisen for that matter. Of the Gaim/Toqger summer episode!

And if they aren't separate worlds.. Then why the heck aren't older Riders helping the newest ones? They don't all lose their powers. I know I know it's in the script.

My theory has always been that the pre-Decade Riders were all on separate worlds, but Decade brought them all into the same world. Kinda like what DC's Crisis on Infinite Earths did.

As for why they only show up in movies, I'm going to assume that it's like the Showa era and they're all busy fighting evil in South America.