The best is to get a 1-2 yrs old mint condition used M3, so you get both of the worlds.
Everyone is different, and some people may regret not getting the M sooner, but others may regret not saving enough money. Bottom line is, although life is short, but it is never about how much you make but how much you save. The older you get the clearer you will see how beneficial it becomes when you add up those little savings from skipping a Starbucks or dining at home or not going to the movie theater.
And, being less relevant, you may love your M but I doubt you will love BMW's dealership services... Trust me, BMW's service does not live up to its price tag. So you may get buyers remorse not from paying a brand new M but the crappy brand equity that comes with the car, lol....
Get a used one and be familiar to BMW as a brand so you can accurately set your expectation and minimize your buyers remorse.