My approach is quite different. I like to come up with some ideas, build a proof-of-concept working model out of inexpensive material. test it out in real life, and then maybe rebuild it with better quality materials with the new improvements.
I agree with thinking through a project up to a reasonable point, but until I actually put a model to the test in real life, sometimes you just don't know how it will work. Then, I can see what needs to be changed to make a better version 2.0. That works for me on new idea projects.
If you are lucky, you might find some ideas that have been around for 50 years, or more, and then it's just easier to accept what have been proven to work. I don't have to reinvent the wheel.
I spent over a year looking at many, many, chicken coop designs before I built one. I really like it, however, there are things that I would change now that I have lived with it for 4+ years. Mostly small changes, but things that I would build in differently based on now knowing my needs.
For example, I made a drop-down panel in the back of the chicken coop to clean out the old bedding. I load the old bedding up into my wagons and haul it into the chicken run for composting. A more efficient system, for me, would have been to make a drop-down panel directly into the chicken run. At the time I built my chicken coop, I had no idea that I would later convert my entire chicken run into a composting system. My original idea was to haul off the old bedding and dump it into my pallet wood compost bins.
It would be good to know examples of what you are talking about. What have you found you wasted money on?