There are several questions here.
- Whether I can find a car that does everything (I suspect not).
- Whether I should drive the sports car everywhere (I suspect not)
- If I get two cars, what kind of commuter makes the most sense
- If I get two cars, do I get what I really want to drive? or do I get an NSX and view it as an investment.
Here's my 2 cents, speaking as a guy who currently owns 5 cars and will soon be buying a 6th:
Cars are tools. If you are serious, you want the right tool for the job. I definitely urge you away from the "universal" car because while it
may have the cheapest buy-in it is the least satisfying route.
My wife and I own 2 daily driver sedans - 325i and TSX. I enjoy driving a 3-pedal manual so the BMW is a stick and her TSX is an automatic (incidentally, one of the nicest I have ever driven). Neither are sports cars but both are athletic enough to be entertaining and deal with the daily cut-and-thrust work well. Both deliver in the mid-20s for gas mileage. With maintenance both will last towards 200,000 miles.
We also have a 10-year-old minivan that cost little to buy, nothing to maintain, and hauls a boatload of crap anytime we need it to. It will likely last the rest of our lives performing its infrequent duty whenever needed.
We have a 2002 Impreza wagon, which is a good utilitarian car for my 18-year-old daughter. Rugged, reliable, holds a bunch of stuff, and is a decent drive.
Lastly we have the weekend car, my old '67 Pontiac LeMans convertible - a good weather boulevard cruiser. This hasn't been driven much lately because I'm no longer really interested in cruise nights and car shows, and it will probably get mothballed in the near future.
I have been autocrossing my 325i for the last 3 or 4 years because it is all I had that was remotely up to it, but the 3er will never be competitive even in stock class. So instead of spending a lot of money on it and having it still be a compromise solution, I'm most likely buying a dedicated sports/competition car in the near future. The 3 will last another 10 years as a DD if I need it to, and if something happens to it, I'll get a similar used car that's meant to be used.
I don't know what to advise you on the NSX. That depends mostly on what you want out of your toys. Cars are depreciating liabilities. The best way to protect your investment is to pick a great driver's car and then keep it in the garage and never drive it. If you have a lot of mint-in-box original Star Wars action figures in a closet waiting for the optimal time to sell them on eBay, then that may be the right route. For my toy, I'm buying something simple and cheap with good performance that I can flog the living crap out of and not cry blood about if I thump the tire wall on a track day. If you love the way the NSX drives, then buy one and drive it and don't look at it as an investment.