This has been interesting to read. I think the big thing I go for is "does it look more-or-less like it's supposed to look?", and "Is it something that if it were 1:1, I would be embarrassed by if I said I had anything to do with its assembly?"
My builds are far less than perfect, usually. Most are box-stock, or box-parts-swap. Someday, I will successfully wire an engine, and I think I figured out how. I just need to find a car I want to try it with.
It's funny...as people usually look at the exterior, I'm finding myself being drawn more and more to restoring old curbside annuals, so it forces me to work on things like coachwork presentation and the interior. That's what people see, and as much as I want to be happy with my own builds, I want people to who see anything I build and be surprised or delighted by something because everyone deserves to look at something that's actually worth looking at.
But, in the end, you must be the one satisfied. You are the customer and the contractor, both.
Reminds me of a story I heard when I was in college. I don't remember where I heard it at the moment, but it was an important one.
An old carpenter was skilled and did his job well, and his boss gave him his most challenging jobs. As the time for him to retire came closer, he was getting tired, and wanted to go enjoy life, when his boss said "I need you for one more job before you retire. Do you mind?" The carpenter wasn't thrilled, but agreed to do it.
The carpenter was tired, and decided to not be quite as fastidious. A couple of corners weren't quite sqaure, structurally sound, but not square. Some of the finish work wasn't as clean as he usually worked. The exterior had a couple of minor flaws. But, the house was completed, it was sound, and the carpenter was tired and ready to rest and enjoy life with his family.
His boss came by, inspected the house, and handed him the keys. "This is for you, as your retirement gift, and as a thank you for all the years of hard work and dedication to me. Enjoy it for many years." He shook his hand, and went his way.
Suddenly, the carpenter felt not so easy, and more than a little ashamed.
Moral: you'll know what you did right and wrong. If you have to fudge something, make sure it's something you can live with.
A little something to keep in mind.