Hi Colin,
I have had my +2 zetec for nearly 3 years now and still love it; I tell anyone who will listen that it is a very practical alternative to a modern Elise, there's so much more room and the performance is very similar including the twisty bits, I regularly put Elise's and Exiges to shame on track days.
There are a few downsides to the conversion as you mention (nothings perfect), the clearance of the exhaust manifold is a particular issue when negotiating speed humps and poorly surfaced back roads, I have a sacrificial skid plate welded to mine and raise the ride height by 20mm using the adjustable spring platforms for road use, when on track I lower it a little although the compression at the bottom of Paddock Hill Bend at Brands Hatch is a problem meaning I have to leave it at road height or risk a black flag for trailing a shower of sparks
Performance wise I have a gas flowed head, raised compression and racier cams which is supposed to put out in the region of 190 - 200 bhp, it's been rollered for a power run only at 193bhp (no alterations), so I was happy with that although I did feel the car was a bit light on power when driven, Andy at Spyder says that the +2 Zetec is a
'Deceptively Quick Car', by which he means you are accelerating and going an awful lot faster than you think, this is a good theory I think as I am always wondering why everyone else is driving so slow on the road and Elise's are easy meat at Castle Combe, you just need to get the line right going into a corner and next straight you are powering past. I had the valve/cam timing altered about a year ago which made the low rev pickup a lot peppier, ask Andy at Spyder about this, it's worth getting him to do it for you and makes the car appear more powerful. Leave the Emerald map well alone unless you really know what you are doing, probably best to book a session at Emerald although you will have to wait a few weeks for a slot.
I changed my fuel tank for an aluminium item, it holds 12 gallons approximately and the fuel light starts flashing when there are 2 gallons left which is a useful reserve. I get about 40mpg on a run but this can go down to about 32mpg if I?m pressing on..... track days are best not mentioned for fuel economy
Regards