yes, resurfacing is just a tiny bit of weight. when you shave it, you remove enough of it to significanly weaken the entire structure of the flywheel. your talking somewhere between 5-10 lbs being taken off for a noticable gain, thats half of the weight of the flywheel. if you take any stressed part of a car and reduce its weight (from the factory) by half, your gonna be pushing it. if you shaved 50% from your con rods, how strong would you expect them to be? or your pistons? block? etc. the difference between resurfacing and shaving is like the difference between sanding down a 2x4 and ripping it into a 2x2. the more mass a flywheel has, you also have a given heat absorbtion. the stocker is meant to have all that metal there to absorb the heat, so it doesnt have to shed it as fast. shave it down a lot, and you lose half of its heat storing capability. subject it to the now higher loads of it being lightened (higher revs to start up) and you have significantly more heat. that heat warps the stocker. thats why only aftermarket light flywheels are safe at their given weight, they were made to shed heat faster, given their lowered weight. if a flywheel is lightened incorrectly, ie its out of balance by just a tiny amount, it will cause lots of shaking even a slight imbalance at the rpm's the fly sees is a recipe for drivetrain soup. same with warped flywheel, it shakes the whole drivetrain to death. a lightened flywheel can be fine, there are lots of people using them just fine. but if the stocker has any sorts of imperfections, if its done incorrectly or poorly, or if you just drive really hard, your taking a big chance of ruining a lot of parts. ive heard of cranks, clutches, trannys, blocks, etc all being ruinied and traced back to a poorly shaved flywheel. i just dont see it possibly being worth it, when the cost of an aftermarket unit isnt that much more, and frankly, neither really does anything for absolute performance (driveability is in the air, ive heard positives and negatives)
as for turbos, i think your wrong. a person who knows what their doing can do it themselves. if you know what you want and get a properly sized turbo, either new or rebuilt, you will be fine. only think i see that needs to be done at a shop is fuel tuning, with a real tuneable ecu. a hondata (cheapest tuneable ecu) needs to be done by a pro, but the rest of the parts dont need anything more than someone mechanically inclined with a good set of tools. besides drilling the oil lines, just about every kit is more or less bolt on. shops dont know anything we dont, all the information anyone needs is out there, you just need to find it. ive spoken to many shop people, and id be terrified to hand over my car to have them do work on my car- not a single one ive ever talked to me knew any more about anything than i do, and theres a lot of things i dont know about. i know there are shops that could blow my mind, but nothing ive ever come across, and from what ive heard, thats pretty much the sentiment across the country. finding a truly good shop is very difficult, and i see no reason why a well read person cant do their own work on a turbo.