MPG depends on drivig style and distance. A 4 mile trip barely gets the car to full operating temp. so for most of the journey the ECU will richen the mixture like a choke on normally aspirated cars.

I have 2 Sporties and have owned one since 1994 and get 32 to 38 with 40mpg on long runs. I don't race the car as it isn't a Mini and I tend to cruise around 70-75 on Motorways. The best MPG is normally at 3000RPM. Bare in mind that these are quite heavy vehicles.

K&N will improve performance a bit and MPG maybe. The ironmongery of the original Air filter system slows air flow and alows it to warm. The theory now is that colder denser air increases the combustion amount of fuel and air mix. I tend to agree with this. The normal Air filters last for many miles and I had one on for 100,000 and just blew it out with compressed air at each service.I have now gone K&N on both my Sportraks to allow free flow of colder denser air. Yes the induction is noisier and perhaps acceleration a bit better, MPG is not much better and will be worstened if you like the induction noise and become more heavy with the right foot to enjoy the noise.

The ignition system is often ignored because it is electronic but the leads can fail and cause poor performance and MPG over a period and eventually cause bad starting. The problem is that the conditions they work under are quite hostile and the modern carbon fibre leads have mall breakes in the carbon to force the power to jump across gaps increasing its intesity. Great when in good condition. As the insulation fails, these gaps become damp and the leads performance is affected. Like wise although these have electronc ignition they still have a dissi cap and rota arm that both wear but are, like the leads often overlooked.

As for plugs, I use the normal single electrode type, either Bosch or Champion. Living in France choice is often non existent so I get them from ebay in sets when they come up for sale. I haven't tried the multi spark type so can't comment.

The Sportrak is not a "boyracer" vehicle, no insult intended, and if you are heavy on the right foot MPG will go down parcularly on short journeys. Cruising at about 3000RPM on a motorway sould give a good return per gallon of about 40mpg. Start racing up to 4500 and above and you will notice the difference. I've owned one of my Sporties since 1994 and done 100,000+ miles in it. I've towed car transporters with a Mini on and a box trailer and never got down to 20mpg. I suppose my average MPG has been 35.

Hope this helps you

OLDMINIMAN