OEM keycaps on the Filco are etched ABS, correct. Geekhackers tend to get crazy about keycap materials and whatnot, but the truth is that even "cheap" abs caps will last practically forever. They will definitely get shiny eventually, but that hardly affects their usefulness.
Heavy, metal cases make the keyboard feel more solid and that is a good thing. If you're considering the investment, I'd suggest going full custom if you have the money to get it done right. They are programmable and highly attractive. Otherwise, wrapping a Filco in a metal case is just fine, but if you are going to be taking it apart to customize it, please get one of bpiphany's controllers. It will make your keyboard fully programmable.