Despite as much as people talk about "paying for a name" as if it's a bad thing, it is a thing. If you want to sell guitars you build, you'll have to put your own name on them and build a reputation to the point that people are willing to pay for your name on the guitar because it represents a known value. One of my guitars is a '77 Les Paul I bought new in '78, and it plays as well as it did then and (gasp!) I've never had the neck adjusted or the frets worked on because it hasn't been needed. My point is, I pay good money for a guitar that says Gibson or Fender or Ibanez because it's a known product that I can predict will probably continue to be good for a very long time. Your "partscasters" are very much an unknown. So even though someone may understand the time and care you put into selecting and assembling parts and be willing to pay for that, when that person goes to resell it, where's the name? In the end, and in general, people are only willing to pay for guitars based on the value of what they can resell it for.