Great little cars - I'm running a 2006 Mk3 with the 2.0 engine. Unlike the Mk2, its quite happy to cruise around and feels stable and secure on the motorway. Its definitely a car you could use everyday. For me the 2.0 was essential and you would want a Sport model because that comes with a 6 speed box. Bear in mind that until recently very few MX5s came with air con and whilst that's not important when the roof is off, in a warm wet Britsh summer its a bit of a bugger.
I've no idea of mpg because its a third car and I hardly use it. Mines a soft top so no real idea about the folding hard top either.
Of course the best bit is the rwd handling and feeling and lightness and directness. Its not as pure as the earlier models but that's the price you pay for its civility. You'd want to fit the lowering springs from either Mazda or Eibach as Mazda simply jacked the car up for European markets to meet safety regs without altering the rest of the suspension - the lowering springs bring it back to the correct height it was designed to be (the car isn't slammed and doesn't trouble speed bumps) and improves the handling no end.
The 2.0 also has enough power to unstick the back end which comes round surprisingly easily in the wet but there is switchable ESP to keep things in check when you're not in the mood.
You're always welcome to pop over for a coffee, chat and a drive if you want, Stan.