I don't have any bass regrets, I wouldn't mind having my Mayones custom Be4 back as it was built for me and I recorded my old band's album with it, but to be honest don't miss it.
There is an amp I'd like back though, I traded my EBS Fafner with Shep on here when we moved to a smaller house, I didn't realise I wanted it back until he put it up for sale.
I considered buying it, but better sense prevailed and I resisted; just got myself an HD350 though, so that's keeping me very happy.