I'm still transitioning from X1 to X2. Any new projects I start on X2, but I've got an album on X1 and don't want to switch it over till I'm 100% happy with X2 stability as I had seen some issues on my system.
I do notice multiple things when I'm on X1 working on my album where I wish I had it switched over to X2. The track zoom feature is really handy. I'm looking forward to properly using that. What it basically does is say you have 20 tracks, all of them are minimised but just activating one by clicking on it zooms it up to your last set size. That I don't care about so much, but what I do like is that if you re-size all the NON selected tracks, EVERY single one resizes to the same degree. So you can easily resize ALL tracks to the same hight to keep them small, but still give you access to what you need. It basically suits MY workflow. Others work differently and it wouldn't assist them in that way.
The ProChan is greatly upgraded (unless you had X1 extended, which I don't). More customisable. The LA2A plug is AMAZING!
I'm still used to comping in layers so I don't know how I'd like doing it in X2 with the take lanes.. I don't really like the new selection bar on clips either. It's much smaller and harder to move clips around.
There are plenty of other things but those are the main for me. The ProChan upgrade is probably my most useful one. It was worth it for me. But if you don't have things in X1 that are really bothering you, there probably isn't too much need.