If this is your very first track day then I would recommend just the simple stuff like brake pads, oil, water, tyres. Bushes, suspension changes and all that can wait. Until recently I had a Westfield that i used for track days but sold it and replaced it with the E30 sport. I then had a day at Donnigton having just put new pads on it and the car was absolutely great, not as fast as the Westy but full of communciation, fast enough and definately confidence inspiring. My car would benefit from new bushes, better brakes, stiffer suspension etc as would everyone elses however I reckon it would be better for you to put the money into several track days first to learn the car, see if you enjoy it and only then start thinking about modifying it. Owning the Westy did teach me something; There are people who pile money into their machines only to look at them and there are those who just drive 'em.
Just enjoy it.
Scott
