Well, the idea of a sleeper car is that it looks stock, and/or beat-up, but has an insane amount of power under the hood. I could never be happy driving a car that looks like shit, so mine will not be beat-up.
The styling will be almost stock, with some minor changes to the body because of the extra length I added. Carving in some understated wind channels to increase aerodynamics, angling the bottom of the front bumper for aerodynamics, and the rear bumper for wheelies (like I said in the last post), adding a carbon-fiber skid plate for aerodynamics again, lifting the hood about two inches to allow for the bigger engine, lowering the suspension for extra handling. I am going to install LED's just about everywhere hooked to different switches, so when I don't feel like hiding the awesome of my car, I can become very visible. Xenon 4300K HID's for awesome (4300K is the brightest, whitest light available). Alternate "fog lights" hidden behind a bumper panel in infrared, red, orange, yellow, green, blue, violet, and ultraviolet. Why two light spectrums humans can't see? Infrared receiver in the windshield so I can turn all my lights off and drive invisible. Ultraviolet because blacklights are awesome, I don't care who wants to argue. As for the rest of the colors, why the fuck not? The paint color will be flat black with deep purple undertones. I don't want any gloss on this thing.
Stripped out interior, back seat removed and the floor panels smoothed out. I might install a massive sound system, but more likely I'll just mirror the floor, pop in a couple 10" subs in the spare tire compartment and 6"x9" speakers in the side panels, both of which I already have from a previous car, and do something funky with the rest of the interior. Obviously, racing seats and harnesses for the front are in order, with new styling for literally everything. Black primary with deep purple accents, touchscreen sound/engine/nitrous control/feedback in the center front panel, override switch in front of the stick, manual handbrake for awesome, and a stick with what will likely end up being a Minecraft Obsidian block for a head.
I managed to find an aftermarket high-performance exhaust kit that has an electronic override to completely bypass the muffler at the flick of a switch, but is extremely quiet when engaged. That will let me cruise around in an understated manner, but when a racing opportunity presents itself, flip a switch and I'm no longer losing power to the muffler....and my 750 horse V8 straight-pipe will make itself known to the world by deafening everyone in the area. I just need to make sure my wheelie bars are strong enough to handle that much power in a car with a curbweight of just over 1,000 kg.
Most people drool over their dream cars. I'm building mine.