I think it's quite rare to have a game where the Goons split matters. I'd be happy to let my opponent take 6 Goons in almost every game if that meant I got more of the draw pieces. It's really hard to play 6 Goons in a mirror match. Getting to playing 4 is even quite a feat and usually more than enough to threaten piles and score a lot of points.
The big ones I have found where the Goons split itself matters:
1. Page
2. Peasant
3. Lost Arts
Page can make the Goons split pretty big, particularly if you are trashing/Page on the opener. You do not pile a lot of stuff and non-terminal goons means you are not out of a second pile once you run the Goons.
Peasant & Lost arts can both make Goons easy to play in quantity, most often by dropping a +action on your draw pile. With even light trashing you typically can draw 6 Goons pretty easily and have the actions to play them (from a village) without piling anything except the Goons.
Exchanging cards, in general decreases the rate of piling, particularly if you are trashing or sifting to exchange faster instead of acquiring cards (e.g. Scouting Party, Expedition, Outpost, Hermit, etc.).
More situational:
3. Tac - you need to play 1 card to have 10 in hand for draw and it is a free action if you chain every turn. This means that you will pile the village and the Goons, but you need 8 buys to go after the estates. You only need 4 Tacs and you can go light on economy with all that draw. With light trashing, you can quickly get to 6 Goons and even if you lose the village split still play more the other guy, and trash out for 4 or 5 VP.
4. Kc - actions do not matter anymore, but you often do not need that many Kc's or anyone one particular card (e.g. 2 Smithies, 3 villages, and 3 cantrips are likely enough to leave you where you draw deck and play a bunch of Goons with more or less even Kc/Goons buys). Trashing helps again but +buy can make 3 pile instantly viable.
5. Herald - huge pile of +actions if you mix in a village (e.g. Bazaar, Lcity, or vanilla Village) in any quantity, and of course you want Plenty of Goons.
6. Wt - Okay, so you need extra villages and you will deplete the Wt pile somewhat, and you can burn off the curses for "free" ... but you can also have games where neither side wants to be the first to take a bite out of the curses and if you have two village piles you might want to exploit (e.g. a $3 and a $5 village) you can watch that curve climb for VP per turn. If Goons is the only +buy, you can then setup a turn where only you can end on it on your next turn.
7. Prssn/Fort. Massive +actions and you will pile a $5 (say the draw like Rabble) ... but again you can efficiently set up for six Goons without touching 3-pile territory.
9. Xroads. Not enough on its own by any stretch, but it gives you extra actions to play without completely emptying a village pile (and it is not like it is a bad play on $8, 2 buys if you want a Goons).
In general, though, I agree winning the villages is much more important for Goons. The more stuff you can play - trashing, draw, other attacks, etc. the better off your Goons engine runs. With Prince, the best thing on a Goons board is that it draws after the Goons hit so you can start the hand with more cards (e.g. Prince of Smithy or even Village). I suspect that in most Goons game Ferry would not want to be on Goons or Prince, but instead on the village pile or maybe the draw pile.
