I only consider it an upgrade due to being technically a younger/newer unit(being I got mine very early), also the LEDs being placed where they are I find beneficial, and also the memory increase -which I never really run into issues with- but I think having a little extra would give me that 1x more effect unit I'm desiring.
I have no issues w/ my HD500 currently, but I am a very active gigging player, with multiple sets, setlists, custom patches and midi sequences and having a backup should always be rule #1. -and have been super fortunate w/ the board so far :)