There are only 3 cars that I'm aware of that look "cool" with sidepipes:
1. 1967 Corvette
2. Early year (1994-1996) Vipers
3. Shelby Cobra
I'm not sure if these cars are really even "cool" with the sidepipes, but at least they get an exemption because their pipes came from the factory.
I'm not saying it's necessarily "right" or "wrong" to have the sidepipes, but unless you're going for a 1970s period-correct car, you might want to prepare for some ridicule. Having a different look doesn't always equate to having a good look to your car. I just don't think the sidepipes will have a positive impact on the overall look of your car.
Spoilers - one word, three times. SUBTLE, SUBTLE, SUBTLE. Think first generation Camaro. Short spoiler, just coming off the back of the trunk, turned up no more than 3 inches. Just kinda blends in with the car. Some folks even mold them into the trunk. I've actually seen a few of these on Novas and I think they really work, but it's because you have to do a double take to even notice that it's there. Anything more than that starts looking ridiculous. Again, unless you're shooting for late-70's period correct.
Flat black - I'm a big fan of flat black (Satin Black)on certain cars, but be forewarned on this, most of the time people will just mistake you for having an unfinished project that you're driving around in primer. It's hard for the casual observer to tell the difference between satin black and black primer. You'll spend a lot of time telling people the difference (which is OK, if that's what you really want to do).
Those of us that live in the 4th Gen world can attest - there are already plenty of 78s running around in primer. If you're going Satin Black, black bumpers, black wheels, dark tint (murdered out) - now that's sinister. If you're not going that far, Satin Black just looks unfinished. It's a subtle difference, but one that does matter, I think.
Good luck with your build. If you're happy with how it turns out, what we think about it doesn't matter anyway.
J