Nick said:

I don't feel a need to get precise measurements off an existing design before using those ideas for something of my own design, but studying a lot of different designs, and using them to see how they perform can be informative for coming up with innovative ideas.

Nick is a modest person and didn't add what i consider to be a critical point:

If you are an expert paddler you will be more likely to do a good evaluation of a design. First, because you have probably paddled a lot of different boats and have something of a 'database' for reference. Second, you will be capable of paddling the boat in conditions (wind, waves, current) where its strengths and weaknesses will be most apparent.

There are 'bad' kayak designs out there - some produced in the thousands. If you get a group of (unsponsored) expert paddlers 'in the right mood' you will hear about bad boats. Fortunately (I guess?) most mediocre paddlers (like me) seldom push our boats very hard, so may not notice some shortcomings. The sad part of the whole story is that the 'bad' boats usually are paddled by novices, while the experts paddle better designs!
How often do you hear a kayak designer (amateur or pro) admit to a bad boat? It's even more difficult if many (many,many, in some cases) hours of work has been put into the project to bring it from plan to a floating kayak.