I don't think they'd be good for more wine. Got any hard alcohol you want to play with? I know that producers of spirits like Scotch will age their new whiskey in used wine barrels. One of my favorite single malt scotches is aged in port barrels, for instance.
I believe the cubes are generally intended for use in the carboy rather than the bucket and can probably be used for 2-3 months, either in one wine or successive ones. I did have a Pinot Noir that came with just cubes and used them in the bucket for that ( it normally is not oaked much) and then put them in a Valpolicella for a couple of months ( carboy). There may or may not be any more benefit beyond this time.