Not really. I think the most compelling reason would be performance, and that is a pretty subtle improvement. Smart previews if you need to edit large numbers of files while on the road with a laptop.
Is it just me, but I am not impressed with the new healing brush. I find the edges often quite visible after healing or cloning. It is helpful for simple edits, like a sky, not not so much for things like tree backgrounds. Again, a work in progress I hope.
I'm left with the feeling that a lot of energy went into fixing LR4, and with a shortened time between releases, not much else got done. So, mostly, you are paying adobe for a performance tweak and some JDI stuff. Even with the performance tweaks, the LR import module performance does not appear to have had an overhaul, and is still a poor second to most image browsers, and not in the same league as PhotoMechanic.