It really depends what your needs are. If you think back to movies like Perfect Storm or LotR or any other notable CG movie from several years back, they were using older versions of Maya in the pipeline. There's a lot underneath the hood even with the older versions that you could spend a lifetime learning. There are nice additions with newer versions but I haven't really come across much I couldn't do with the earlier ones. I've talked to some folks that use the newer versions 8.0 and 8.5 in production settings and have heard some horror stories about bugginess....nice ideas, just not implemented well. If you're going to upgrade, just wait for the new release and see what verdict is.