I have seen example printers that have different colour plastic strip fed into them so you can print in 3d and in colour but wait until they combine inkjet colour printing with the 3d side. It would totally change the toy and model industry business model over night. Lost a few hotels from your...
They already do, the test software for most of the 3d printers will print a spare set of cogs and gears for the printer that's printing it incase the originals wear out.
And I know the cost is high at the moment but remember when colour laser printers first came out and cost well over a grand...