It might be a nice project car if you have access to cheap labor. I paid $3500 for a spare 986 Boxster S engine a few years back. If you can get it inspected and discover the rough running is related to something relatively minor I’d make that trade all day long. And I love Miatas. But the Boxster is a level above.

Just buy a 981 series Cayman or Boxster and leave your worries behind. Very very reliable cars. Not only has my 981 Boxster Spyder depreciated very little since I took delivery 8 years ago, but I never had a single warranty repair and even now after 35k miles nothing has malfunctioned on the car.

You are asking the wrong question. The real question is “at my level of driving skill am I able to discern a handling difference from a 1999 base Boxster and a new GT3 RS? (Presuming you have no track experience).

In my 2002 Boxster S, with only suspension mods, I regularly left “Advanced drivers” from other parts of the country in the dust at Sebring raceway at winter track events they attended. The difference being it’s my home track. I have thousands of laps there over past couple decades, and they are experienced at other tracks but unfamiliar with Sebring.

My point is that Boxster has all the handling capability you will ever need or be able to realize safely in a street scenario. So buy a newer, “better” Porsche for other reasons, but not for handling reasons.