Why don't you think it - the concept of a TREK team up - would work?
I'll admit, I love Generations. It's my third favourite Trek film after TWOK and TUC. But even I think the teaming up of Kirk and Picard was overhyped and ended up being a bit anti-climatic. All it really is is a soul-searching horse ride and then they tag team to kick Soran's ass. I mean yes, I like these scenes, because they enojyable scenes not because it features two captains teaming up.
Honestly, crossovers have limited appeal to me. Sure it's a nice novelty to see characters from different series meet each other. But after the novelty wears off there's not much to it. And really, I found the movies featuring each of the heroes that comprse the Avengers more interesting and entertaining than The Avengers itself.
All you'd have to all Treks teaming up is just the novelty of characters meeting from the different shows. Which we've already had from all the various crossovers on the different shows anyway. Hell, Picard has met every other series Captain except for Archer.