Actually, there are aspects to those cars which show why modifying cars needs to be done in a very thoughtful way.
The law of diminishing returns is very clear in all three of these cars.
The D3 Caddy cost over $50,000 and while it's braking and handling numbers were a significant jump over stock (60-0 109 ft vs. 128 ft. 80-0 192 ft vs. 229 ft, .87g vs. .84g 68.5 mph slalom vs. 62.

it's straight line prowess is nothing to write home about (0-60 6.1 vs. 6.6 1/4 mile 14.5 @ 97.8 vs. 15.0 @ 94.2)
A used 2005 model CTS-V would likely cost about half that price and outperform it in nearly every stat. 0-60 4.8, 1/4 mile 13.2 @ 109 mph, 60-0: 115 ft. SkidPad: 0.87g Slalom: 66.0 mph. And if you put Toyo R88 tires on the CTS-V you can bet the braking and handling numbers would drop significantly. Hell, the new CTS-V (which is an amazing car and would beat the D3 in every stat starts at only $59,995 MSRP!
The Spoon NSX was $500,000! While I'm sure you could get that price down, there is very little point as just the cost of finding, modifying and keeping an NSX is a huge money loser. I always liked the NSX, but it was never a top level performer, even in it's heyday. You'd be much better-off buying a stock 911 turbo, GT3, or GT-R over a Spoon NSX-R.
The Techart GT Street is $250,000 (twice the price of a 911 turbo) and improves little over the stock model, and actually looses some lateral and braking prowess in the deal. For the extra $125.000 why not just buy another 911 turbo and strip it down to race weight, throw on the same tires as the Techart has, get a tune and you would likely see better numbers.
The Mine's GT-R is a very questionable call indeed as it jumps the price by nearly $80,000 for a .1 second improvement 0-60 and .3 in the 1/4 and .03g lateral, while loosing almost 2mph in the slalom and adding 5 ft of braking from 80-0.