I've got a 172 that my wife uses as a daily and we both use for track so it looks standard with no stripping or anything including standard seats but I've got FK Konigsports fully adjustable coilovers, braided brake lines, Brembo HC discs and ferodo DS2500 pads. This is sufficient on its own as they handle superbly well out the box.
Other mods I've got and are recognised as the best for the money is a Whiteline rear ARB, RS tuner remap to increase red line, spread the torque and reduce the pathetic fluctuating idle.
15" tyres for track with track tyres do wonders. Just be aware of Cambelt changes at 5 years. They can be expensive and will require aux belt, water pump and Dephaser pulley on its second change.