Nice try, but when we see the PD invoked in modern Trek, it's invoked for ideological reasons, out of a belief in non-inteference, NOT out of a fear of the logistical difficulties that interference would bring.
Which doesn't mean those difficulties don't exist. Big picture here, folks.
Besides, don't forget that cultures they help are also potential new allies, just like in the real world, when countries that get humanitarian aid from another country tend to view that country more favorably. Even from a realpolitik standpoint it makes sense.
If they're advanced enough to be of any real help as allies, then they can ask the Federation for assistance and it is no longer a PD issue since there was a formal request for aid.
If not, pardon me but I don't think pre-industrial (or even post-industrial) civilizations are going to be much aid against the Klingons/Romulans/Cardassians/Borg/Dominion for a few decades (and this is IF the Feds decide to just hand over technology by the bucketloads).