So, i have looked up "Petty", because i felt something was off with the name. Looks like it is usually a negative word, meaning "narrow-minded" or "irrelevant". Not sure that's what you intended.
Either way, i think we played three games, one of which, thanks to Jack, Hoard, Soothsayer and Apprentice, had me ignore Petty Lord completely and still win. Though, i think back then Robber Knight only gave out a Ruins when you also trashed two cards. Either way, the interaction on that particular board was very good, and i think all it does is prove that you can't always win a game with Petty Lord alone. Because, my problem with the card is how overly dominant it is. Not only that, but as Petty Lord is also relatively complicated, having it be dominant basically forces players to play a complicated strategy whenever it is on the board. It would be far more interesting if deciding whether or not you want to go for Petty Lord was less trivial.
The first thing to get there would be removing the second Action, in my opinion. Petty Lord doesn't need to be a Village. It also doesn't need that awkward ability, which makes sense with the remaining cards of the chain, but also has the card appear very self-centered. At the very least, you don't need both at once. If you buy it as a Village, huh, why should i do this supply pile thing. If you buy it for the Traveller Chain, the Village is just too automatic and makes it far more important than it needs to be. Also the Village shifts it away from the card's central point, the two Traveller routes. Also, it's not like a board with Village-less Petty Lord can't have another Village you could use to create terminal space.
Actually, i don't even like that you can use the ability to exclude other players from upgrading their Petty Lords. It feels unfair on a certain level, and adds yet again to the self-absorbed-ness of the card. If i was you, i would try replacing the card completely.
About the other cards, i think they are fine. I also like the symmetry, and how the conditions are "empty" and "trash", which helps remembering. There's a lot i like there, but i allready told you that. I especially like Protector. Also i like how you have to wait until you get those two final upgrades. That kind of thing's not there yet in Dominion. But Petty Lord...