If you consider the price for an upgrade to be a lot of money then no, it's not worth it. If you've got a six-core @ 3.45 GHz right now, the 8-core Haswell-E isn't going to be that much faster. It might cut your 6 minutes into 4-5 minutes. Is that really worth two grand?
Exactly my thoughts - Upgrading from a 6-core i7 (maybe even a 4-core i7 - like 4770/4790) to the new 8-core is gonna be pretty much some kind of a "sidegrade" for Corona. You might get something in the line of 25% speed increase (tops) for 2 grands. I wouldn't consider it an upgrade if it wasn't a dual Xeon setup.
Anyway, in the end, if you got some money to spare and you like to see any kind of improvement with your render times (and you will definitely), you could probably go for it. It won't disappoint you for sure - But it won't make you extremely happy either.
