What? Do you think being allied with a militaristic CS isn't good enough? XD If you dislike the units they gift you, gift them yourself to another CS to increase influence. Gift all of them to the same CS if you want it to rock! So, in a sense, they are providing you units to fight with or means to befriend other states.
If any militaristic CS gave you all those unique units, you won't have any reason for another militaristic CS ally. Just one and you are golden.
Militaristic CS are giving you mostly science, which is rather good. Free science with no extra cost for having more cities. The only backward thing for me is that, if you lose friendly status for a while, then you have to begin the count again for the next unit to be gifted.
Unless people agree that militaristic CS are too weak compared to the others, I don't see this change needed. As ElliotS, it might be interesting for one mod, maybe, where balance is not an issue.
TIP: Build all your XP buildings in the closest city with your militaristic ally, where gifted units spawn.