I didn't like what Ivy was in SC4, and you know how I dealt with that, haha. I quit. If you don't like her or the game, why play?
I'm not sure if you're asking my opinion on having to be sharp all the time or the time commitment to doing so. For the first one, that's actually where the fun is for me. Needing to eke out every advantage possible to compete, and then having to do it in a high pressure tournament setting, forces me to be a smarter, more confident player. I'm not really concerned about my position in the scene; I just want to play the game at the highest possible level.
Regarding the time needed, aren't you better now than you were in SC3? Think about it. Fundamentally, the game is the same, and you have such a good framework of how to play. All it will take are tweaks and exposure to the new stuff and you should be fine. It won't take as long to tweak as it did to build. That being said, if you're questioning whether it's worth it, then it's probably not. I like having a familiar face/name in the Ivy forum to help me test and find new stuff, but do something you enjoy instead. Either the fire will come back, or you'll find that you don't miss it at all.
And I'll have to concede that 3(A) should stun on CH. Tried to make it work, but ... no.