As long as you have a cIOS installed you lose no functionality that you could have on 3.2 and you gain the sd card menu to alleviate the storage problem slightly if you have a lot of vc games. Even if you don't have cIOS installed beforehand, it can still be gotten on a virgin 4.0 Wii by using the Trucha Bug Restorer to get the trucha bug back in IOS36 and then running the cIOS rev13a installer using IOS36 to do a network install. About the only thing that wouldn't work is starfall on 4.0, but that is outdated and outclassed by startpatch anyways which only works on 4.0 (and 4.1).
Also downgrading boot2v4 Wii's = brick.
And the only thing 4.1 will do beyond 4.0 is fix a bug in Wii Sports Resort that makes the motionplus tutorial video play when you start it again after any time you use the sd card menu to play a vc game.