Hi Andrew, well at the end of the day, a car is only worth what you are prepared to pay for it, and if it's in clean condition you'll get a lot of car whatever the price. If it's any help, when I bought my ZT 180 SE with SE pack Monogram back in 2010, I paid around £4000 for it.
The engine itself doesn't need for any mods really, just make sure the Power and Balance VIS motors are working properly. We have a club VIS tester available and that very nice Mr Stocktake who can set you on the road to some working motors if you find they are duff.
My 180 is extremely powerful and responsive when I put the pedal to the floor, more so than my V6 75, but then it's designed to be different for that reason.
When you get it, be sure to post some pictures so we can admire your new ride.
