IMO: It's ignorant buyers ruining the market.You see it all the time. People put their heart into a car and think it is the best of the best. What people forget is the more mods to the car that are done the lower the value is.(99% of the time). Unless it is like a chip foose or a boyd car. It is nice yes. But for that much money someone could buy a much newer and unmolested car with lower miles. You will make much more money parting it out, since that parts used seem to be of good quality, even better if you can get stock parts and cash then put it to stock and then get maybe 6500 for it. By doing that it takes longer but you will get better money for it. Dont get mad because people point this out to you. You never get out of a custom car what you put into it. They only time you really get money out of it is when you doing a classic restore, etc...
100% of the time it holds true that the value drops with mods... to your average joe looking to get into a civic to save gas money, and have cheap maintenance.
To an enthusiast, it should be looked upon (to an extent) as "i couldn't build that car for that price", even if you're paying more up front; in the long run you're saving money.