IMO the aluminum spacers allow YYF to cheaply manufacture a plastic yoyo that has the consistency of aluminum.
Without having the aluminum spacers the quality control would entail them having to check the bearing seat on every yoyo that is made, testing them by assembling and throwing them to ensure the bearing seat is working proper. Maybe that is a but overboard, but IMHO it would take a lot longer to QC the yoyos if they had a molded bearing seat.
A for the tight fit, yes its a bit off a pain, the first time you deal with it, after that it is pretty easy to separate them, and again, the tight fit is too ensure a quality playing yoyo.
Would the yoyo play as well with loose fitting spacers, it might, but it also might not, by keeping the tolerance as tight as they possibly can they seem to be trying to ensure a longer lasting tight fit, and a better playing yoyo in the long run.
For people that are really bothered by it, it is possible to make the fit looser on your own with a nail file, spend ten minutes scraping down the bearing post on the spacer, and you ll have a loose fitting spacer.
Have fun, and good luck.