Buying a new version of JRiver is not like buying other software. You pay on a subscription model, and your payment allows you access to the next year's worth of updates. Your current version won't stop working if you don't upgrade, but it also won't benefit from new features. The catch is, we don't know what those features will be yet.
You can view every improvement, fix, and new feature added during the last year
here, and it's frankly a pretty decent list. Big ones for me were real time DSD output conversion, R128 volume analysis, DSD format conversion, and XBMC-format .nfo tag recognition. I use at least one of those things daily, and I'm looking forward to seeing what new features they come up with this year.