If you have a dual terminal battery with both top and side terminals, plastic caps on the top posts could be beneficial in case a grill or tool is dropped on top. For side posts, you should have no problems so long as the battery hold down is in place. The Fiero didn't come with any formed cover made onto the cables, so GM apparently felt there was no real safety issue. Lots of side terminal battery vehicles have no shield over the terminals.
If you have unused top posts and really want a pair of caps to go on them, I'll see if I can't get a couple from the local battery manufacturer where I buy my batteries.