I have always done a reset after an OS upgrade and I believe it helps by getting rid of the inevitable bit's and pieces that are left over from the previous OS.
I also do have a lot of stuff I don't use disabled and I'm certain that has helped with my speeds and battery life. See my battery stats thread below.
Post Your JellyBean Battery Stats
I know that doing a reset can be a complete pain in the rear, but if you don't do it, you're not going to find out if it helps or not.
If you do a reset and you still don't like JB, then you can easily downgrade back to ICS using pc-odin.