Hi bonhamsurf,
Well, what's done is done in the past. No point in punishing yourself by thinking " I should have/could have done this or that...." Of course hindsight is 20/20. But life is very murky and we have to make choices based on intel. data at that time. Since life is dynamic, you need to be fluid and flexible. It's ok to change your mind, that's part of being fluid and flexible. The cost of course is time and money.
You didn't make a wrong choice in buying the M3 and trying to upgrade it. However, the situation has changed and now you want to have a NSX in your life. So, let's do it. Sell the M3 and parts and generate the fund so we can start looking for the best NSX you can afford. The quicker you start this process the better.