Not my adage; I just absorbed it from the community. With coin tokens,
Spend early, save late.
What this means is that early on you should spend your coin tokens as much as needed to get the best possible cards for your deck. Towards the end of the game, save them up to either get $8/$11 every turn consistently, or run your engine until you have enough coin tokens and buys to buy all your green in a turn or two.