Time to sell my dvd collection?

If you want to replace them with HD when they're available then sell.

If you don't watch them anyway then you've answered your own question notwithstanding the HD situation.

Hard to understand why you'd consider keeping them if they'll be obsolete, and you don't watch them anyway.

I agree with you Holeneck - HD will take over within some time (let's agree to look back at this thread and laugh on 2 May, 2011), but the process will be painful thanks again to Sony.
Elcasette, Beta, SACD - how many times do they need to learn the same lesson? As usual, early adopters will get burned when everything shakes out but that's the norm for an early adopter.
Even most HDTV's today don't have the 1080p required to use everything an HD player can offer.
But back to the original question, with upconverting DVD players available now, if you like what you've got, just keep it unless there's a have-to-have in HD like Cream, Royal Albert Hall, May '05 with uncompressed audio and video.