I've added neem to my soil once. Horror story: there is a crack in my garage floor, it goes deep. I didn't think much of if until I had 10,000 termites come up from that crack in mid-cycle. What a mess, the shop vac handled most of it, but I wanted to make sure they weren't using my pots to reproduce. So I watered in a little neem, no sign of termites, and I've cemented the crack closed
post edit: does 1 tbs per gallon seem like a lot of neem? I usually feed 15 to 20 gallons, and that would be almost a whole small bottle.
Neem meal seems like a great (inexpensive) way to accomplish the same thing.