"Fed up with" and "staying focused" are the two key elements for me from your statement. I have found that I get less fed up and stay focused better when I put less customization and fabrication into the model. That's where I get into the most trouble. I hit a design issue, a fitment issue that came out of knowhere, or a "that doesn't look like it did in my head" issue. All those will end up back on the shelf for years sometimes. If I can come up with an idea that inspires that doesn't require a lot of re-engineering, I am much more successful in my modeling. Choosing the right kits plays a big part in that too. Some might think of that as a cowards way out, but to me it's a choice between something under glass and not in a box.