Brakes are relatively cheap - they benefit laptime, safety and maximise time on track too. Within reason G172/CS could help you pick a brake pad compound that'd be fine on the road too, so if it's a daily you loose nothing in terms of practicality.
Weight reduction - free acceleration, braking and cornering performance. Also just having all that extra noise will make it feel more race-like and add to the experience. Obviously not great for daily use.
Have your alignment checked, maybe consider rear correction spacers & camber bolts up front - this will not only allow your tyres to work properly on track but will make sure you get the most miles out of them. Again overall quite cheap.
Not forgetting making sure the thing is running 100% spot on as it should. Oil/filter/plugs/air filter in standard airbox or "ktec style" exposed filter. These engines & gearboxes love regular oil changes. Spark plugs have usually had their day way before the service interval suggests as well.
If you must touch the suspension, simply refreshing OE parts (a set of cup dampers is something like £160 all in from Adam @ Renault Wolverhampton with CS.net club discount) with aftermarket springs (cooksports or eibach) is getting rated quite highly on here.