Must have missed this post, but thanks for the guilt trip Seth, I didn't even have to pack my bags...
Being a former owner of this receiver, it's got a lot to offer and for the money you're likely to get back on it, you may want to hold on a bit longer. I was able to sell mine (I think) about a year and a half ago for a little more than $300, possibly $325. For the feature set it has, power capability and rep, I'd say you should be able to come close to that figure, maybe a bit less but not too much. If you do have to come down too far, it might not be worth selling.
Depending upon your listening environment, you can always use it as a pre-pro or to power your surrounds and add some external amplification to your front soundstage if you're looking for more oomph at higher listening levels. This might help open things up at loud levels, but from about 80dB and lower, it won't make a noticeable difference.
I'd agree w/Seth though, new speakers are going to make a much larger impact, particularly an LCR set that is well timbre matched and a pair of mains that can give you some good two channel listening for your vinyls. Match them up w/your PB12 Ultra and you'll be set...
-TD