Probably my favorite single thing, which is really a collection of things, is that Python 3 makes many classes of previously obscure bugs more immediate and obvious. hasattr() no longer masks exceptions; object comparisons without ordering methods defined will raise a TypeError, instead of being based on object ID (which is a race condition); two exceptions raised in succession will give you two stack traces, instead of just the last one. These and similar changes make bugs more likely to be found and fixed quickly, during development, instead of lurking until they're deployed. More info here: http://migrateup.com/main-difference-python-3/

That said, it depends on what you mean by "innovation". To me the above is a worthwhile improvement, and more important than (say) asyncio. It's also a "nice to have", in the exact same sense that 2.7's features are a nice-to-have compared to what's in 2.5. At the end of the day, if you want to continue coding in 2.7, that's what you should do.