I have the Uppa Baby Vista as well and we never used the bassinet feature. DD is 2.5 now and I'm pregnant with my 2nd. I found that it was just easier to leave DD in the infant seat and fasten into carseat adapter (though she always wanted to be held so I spent more time holding her than anything). Also, once DD was about 4 months old she wanted to see everything around her. She wanted to be sitting upright and looking around.
I think this is one of those things that really depends on the child. If my next one is different than my 1st child, then I might try the bassinet with her. Also, I think it makes a difference as far as where you live. For a big city or a ton of walking, the feature is probably nice. We use/used our strolling mostly for neighborhood walks and going to the mall, etc.
At this point though, I wouldn't have missed having one.
ETA: My DD was born in early April. This next one is due late March.