Regret is perhaps too strong of a word. But $5M is $5M even if you have $45M. Sure, it won't change your life since you have the $45M, but the incremental investing / philanthropy / estate / family help etc that it allows you is real in absolute terms.

The other thing I've noticed is that for people on the other side of this transaction, it's not like "smaller numbers" all of a sudden become immaterial. $1M is still $1M. $5M is still $5M.

Again, I'm with you, I don't think it's regret exactly. But post hoc you might choose differently, even if it's the rationale choice at the time.