It depends on what tires you are running. Tire Rack https://www.tirerack.com
has manufacturer recommendations for some high performance tires (ex: Hoosier A7: 3 degrees negative camber). Caster can provide additional negative camber on the outside tire when cornering, but can be over done and result in the tire contact patch moving to the inside of the tire and the outside loosing grip. Especially for very wide tires, ask me how I know. For serious work, consider buying and using a tire pyrometer.
There are other suspension modifications available but this depends on what class & preparation rules you need to follow.
Currently on BFGoodrich G-force comp 2 - I've considered getting some really sticky Hoosier's too just haven't pulled the trigger yet. I've also thought of getting some wheel spacers for the back wheels yet unsure how large the spacers should be (5mm, 10mm?). I have approx 19mm of gap from the top of my tire to the inside ledge of the fender. Would playing with camber/caster/and toe affect this? It seems that I should be definitely be having more than -2.0 camber and a large amount of caster (any ballpark ideas to start with?) in complements to a slight bit of tow-in.
Haha, sounds like you have had a couple 'exciting' turn-ins with too much caster...
The car has a few modifications (I won't list them all here) but for suspension mod wise it is sitting on Koni Yellow springs and shocks, sway bars, and a chassis stiffener all from Centerline.