(Contradicting your signature,) I think it's a neat upgrade. I've recently just filled my 64GB, and have other things I'd wish to play on my iPod. With the built-in home sharing, I don't need a 3rd party app for that, anymore. Also, the AirPlay integration into 3rd party apps means that's one less Cydia tweak you have to worry about. But, that's my opinion (which is supported by facts. ).
None of those things apply to me though i suppose i should of said "There's nothing in this upgrade that is worth it for me"
if you can update and jailbreak on the latest, why not, nearly all cydia apps compatible with 4.2.1 are also compatible with 4.3/4.3.1 I don't see a new update on redsn0w, either by the homepage or where their files are stored