I don't regret selling any of the great basses I've owned but, like you, I regret the one opportunity I had of acquiring the bass I'd love to have now.
In the 90s a mate pestered me endlessly to buy his mint Wal MK1 for £600.
I wasn't interested in the slightest at the time because I thought they looked crap.
I was too busy trying to look cool, wrestling along with the pig of a Rickenbacker I owned back then.
£600!! 🤦