A $500 upgrade would be hard to justify, but can you get something back for the HS20? I did a $250 upgrade and I feel it was good value.
I use the EVF almost all of the time, and it is night and day between the 20 and 30. Performance has improved. If you have been reading the HS threads on this forum, you know that user opinion has been mainly positive on the 30, much more so than the 20 received.
For a short answer, I would say go for it if you are a EVF user and you can trade/sell the 20. Otherwise, wait for the HS40 or XS2.