Well,... I think it will boil down to how well you like the sound of your current receiver. Personally I don't like the sound of most Sony receivers, especially the DE line, I feel they are way underpowered, and do not drive the majority of speakers very well. I think just about any receiver from Marantz, Yamaha, Denon, Pioneer, NAD, Onkyo etc. etc. that is in your price range would sound better than Sony. Just "My" opinion.
Is the 7.1 upgrade worth it,... ????? I think that would be up to you.