I'm not convinced Merchant Guild/Goons can by-itself be considered a combo because...
You're usually buying Coppers with Goons only in the end-game, in which case any amassed coin tokens will usually be used to buy green, opposed to useful cards. If that's the case, consider these 2 situations:
Case 1
2 Goons in play and 0 MGs in play -> buying 8 coppers gives 16 VP right now
Case 2
1 Goons in play and 1 MG in play -> buying 8 coppers gives 8 VP right now, and 8 coin tokens -> next turn, 8 coin tokens are used to buy a province for 6 more VP
So in Case 1, you have 16 VP right now and 8 junk cards. Case 2 you have 14 VP after next turn and 9 junk cards. This is obviously a over-simplified toy example, but it seems you'd just rather have more Goons in play.