I'm sure the answer to this differs for everyone, but for me tools have appeal on several levels. First, they are useful things. You can build things with them. This ability to create new things rather than simply destroy or consume them really sets tools apart from many other collectibles in my opinion. I think this leads to tools being a part of the very definition of humanity.
Humans are the only species that have manufactured tools to solve specific problems.
Some other species have developed the ability to use sticks, rocks, etc. to achieve a goal, but no other has conceived of a tool design, carried it out, and used the resulting tool to achieve the goal. The ability to make tools is part of the nature of being human. Humanity has walked down this road from the dawn of time - wheels led to lathes and pottery wheels, which led to threaded parts and assemblies of smaller subassemblies. Tools are necessary to give us paper, glass, houses, and most other items. In time, tools advanced enough to make possible the manufacturing of internal-combustion engines, automobiles, and computers, and in the future new devices will come along.