Car appreciation... the aesthetics, the engineering, etc

They're holding steady/going up in value, they're fun to drive, in your price range, reliable in stock to lightly modified form, cheap to service and easy for the home mechanic should you wish to do it yourself.

There's a reason every track day has at least 2-3 MX5s

If you just want to be a hooligan on A roads, TVR? They can't go down in value any more.