Yeah, Pen Pals and Homeward are episodes where the PD is basically just thrown in to create conflict (kind of like that Season 1 episode where the racist stereotype kidnapped Tasha to be his bride--about halfway through they were like 'This is a Prime Directive episode now!', and it was stupid).
Homeward seemed like a REALLY weak PD justification--I get that it's basically a rough draft of Dear Doctor, and it tries to raise a question (too bad that question is so easily answered). But the fact that, if the society had been more advanced, they would have happily tried to save the planet (like in Deja Q, where they try to stop the moon from crashing, and all of the other gajillion episodes where they intercede because the society is advanced enough to have radio) rubs me the wrong way.
On the other hand, why isn't Journey's End a Prime Directive episode? Why isn't every interaction with the Crystalline Entity a Prime Directive episode? Why isn't The Masterpiece Society a Prime Directive episode until, like, the last 30 seconds? (And at that point, why bother? The episode already asked a big enough question.) And what about 'Suddenly Human', where they decide to disrupt things because it's a human kid (as if they would have happily turned over a teenage Worf if the Klingons showed up one day and said 'He's one of our species, give him back to us')?
And this is why I have a Prime Directive Day, lol.
(Just wish I could have found a good way to work in a 'Good Troi Episode' day, and showed Face of the Enemy.)