The stock set up can be rebuilt for a few hundred, under a grand if it includes new t-bars and sway bars. Add some high end adjustable shocks and you may be at $1500. More aggressive alignment can provide significantly improve feel and performance over stock while having a system that has been proven for millions of miles.

For an additional $4k, you can drop 75-90#, you get quick springs changes, you get reduced turning radius, and get additional room around the oil pan. Just looking at the weight issue, you are paying $50 a pound to reduce weight off the nose. Fiberglass body panels provide a much better value. Springs changes, do you need to change springs for different track? Turning radius, depends. Extra room, that's always nice to have. Is all that worth an extra $4k? They do look cool, which is reason enough for some to justify it. Others will be impressed by it, which is worth it to some. It is lighter, which some people swear by.