I doubt you need more power. Does it distort when you turn it up as loud as you want? If not, then it has enough power.
As for the automatic calibration, that is a good feature to have, but if you are very good at setting things up yourself, it is unnecessary. (Of course, most people are not very good at setting things up themselves....)
While I do not deny that the Yamaha HTR-5990 is better than what you have, I doubt that it would make much difference in actual performance, assuming that you are capable of doing a decent job of setting up what you already have. If you have money to burn, go ahead and buy a new receiver, but if you don't, you might be better advised to spend your money on other things (like more movies and music).
Or, you can wait for whatever the next generation receivers may have (like HD radio, the ability to decode the sound formats for the new high definition movie discs that will soon be available, etc.), and then buy a replacement. If it were me, I would stick with what you have for now. But it is your money, so feel free to do as you please (as if some random advice online would stop you).
