Glad John was able to help you. Get the car and drive it before looking for Upgraditis cures. those tyres are definitely at the end of their life time find some nice twisty roads and drive the piss out of them to wear the tyres out. get a good baseline of how the car heaves with the dead tyres. then try it again w/ real tyres. the bad behavior u didn't expect or like will change.
try the seats out. head rests are available for the s-type seats. if u have plans to plenty of track events then definitely get the FIA roll bar and a seat ready for a 6point harness. otherwise, what u have can last u quite a while and be comfortable. if ur looking for track tyres and wheels get a new set, the prisoner wheels will still be good for blats.
as for cycle fenders, try out the clamshells. if ur afraid of lift, and u can feel it, consider cutting an opening in the wings the way Norm Beaver has done. U'd have to look for pictures back in '07 to see his car. Its a good solution. The color combination is too unique and to quick to bring a smile to start leaving marks on the body just yet.
give it another year or 2