With regards to clears, it comes down to durability. Auto grade clears are the highest in durability, then marine finishes a step below that. For a guitar , that level of durability isn't realy needed, but it's nice to have. As for base coats, in the auto industry, both factory and refinishing industries are increasingly making use of waterbourne technology.... your information may be a bit behind the times. The technology has improved dramatically, but it requires re-training to apply them properly.