I think generally, if the customization is professionally done, and not too extreme you don't ever loose value. It may not improve it, though. I disagree with the idea that bolt ons such as better windscreen or custom foot pegsincrease value, because the bike must have this equipment. The value simply stays the same. Now if you add, say a steering dampener, or adjustable rearsets. this may add value since they are additional features. As far as a cusom pipe goes, first it depends if it is a slip on or full system. Slip ons don't usually add value unless they are a premium brand. Full systems can add value, depending on brand and materials (i.e. Titanum)- but again, the issue is the bike needs this item to function anyways. Custom paint is always a toss up. I would say 90% of custom painted bikes have been down. But that doesn't bother me, because if it is a newer model, it most likely was professionally repaired. I personally am about to custom paint my bike, because i got rear-ended at a red light. All the damage was cosmetic, and I could put factory plastic back on, but I am choosing to go with after-market, with custom headlights and custom paint. Will it improve the value of the bike? Hard to say. I think it will give it a bank value based at least on a prime/excellent condition model. Probably better than the average/abover average rating it could have gotten. Good rule of thumb if you want a custom bike. Buy it that way, if you can find exactly what you want; otherwise, you'll spend way more doing it yourself- but then again, that's half the fun!