Very nice car, ive the 2.0 petrol in a mk2 Titanium and it goes well - so much nicer to have that bit extra power over the 1.6/1.8s. Not fantastic on petrol, but not woeful either - it averages around 33mpg with a fair bit of town driving - the same as my uncles mk2 1.6 petrol. Very reliable too.

I dont know what you should be paying, we paid 7k for a 3yr old 2.0 Titanium with 22k from a Ford dealer (which was a bargain IMO) but now the new shape is out, i would go in a fair bit under the asking price. The Zetec-S is quite desirable though.

Power wise, i dont see why you shouldnt see similar gains to a Fiesta ST tuned - they are the same engine - although I think the Fiesta has a single mass flywheel. I would phone around some established Ford tuners and ask. A bluefin remap and k&n panel filter should easy an easy 160bhp (under 300 quid all in)