James,
If considering an mgf you have the two choices of VVC or MPi. In terms of performance you should consider if the higher redline of 7250 (compared to 6750) is really going to be used. Although the torque curve is indeed flatter for the VVC engine the MPi is incredible close to it in performance until you get to 6000rpm when the engine really starts to wheeze and fade away.
There is also the matter of HGF in the MGF. The route cause of this seems to have been the remote radiator (in the front), something which MGR have been very thorough in resolving in the new TF's. Since Jan 2003 the TF have been fitted with a remote thermostat and water/oil cooler, this together with better HG and steel dowels have pretty much irradicated the problem. Not much consellation to someone buying an secondhand car though.
However, there are certain steps which can make a HG a considerably less agonising experience. The AA have a parts and labour warranty which covers HGF (and other failures) upto £500, which ideally is about the price of a HGF. I've unfortately had two failures but both paid for under this scheme. All I had to pay was £25 excess (and £1800 to Dave Andrews for the additional gas flowing :) ).
I must say in the cars favour, a well set up car does drive pretty well, and is cheap to run. Secondhand parts are easy to come by and servicing is at rover 200 rates. The K series engine as you know, is pretty easy to easy unit to work on, the only buggeration is the rather restricted access.
If buying an MGF be aware that the cam belt should be changed at 5 years or 60K which ever comes first. Some people tend to sell just before the service is due or may possible fib a little about carrying out the work. Ensure that this work is done otherwise it will cost you another £500 for the service.
HTH a little
Tim