I have flown both regular economy and premium econonmy on VS
, and my position is this.
1. Only go for the premium if you can guarantee an upstairs seat (on the 744's anyway), the premium downstairs sucks.
2. Worth $500, hmmm, depends on how much you hate economy. IMHO probably not worth it, a little extra leg room, slightly better seat and a pre-flight drink is about all you get for the difference. Should try and get it on a deal if you can. If you join the flying club, they do them all the time.
Just my $0.02