Regret is like anxiety and worry: they are self generated conspiracy theories. As in other aspects of life, gossip and conspiracy are best avoided - and triple so when the conspiracy crank is yourself against yourself.
I don't think so. Regret, anxiety and worry all invoke analysis which you may not have done otherwise. Sure, too much may be detrimental but so is not enough. I don't think any of these basic common cues are optimal at zero quantity.