Okay, Davio, I'm pretty sure this is not what you had in mind...
...but the following represents a kind of quasi-economics thematic take. I'm not sure this really makes the game any better for you, but I enjoyed thinking about it. As I said before, a lot of the cards would be impossible to make work "thematically", so instead I've tried to make the whole system look kind of like an economic perspective on some sort of agricultural/pre-industrial European society. Sexy, huh?
Each turn represents a period of time, and all the cards in your hand represent the current set of options as to what you can spend time/labor on. Because you have imperfect information about your dominion and investments take time to come to fruition, you are only given a limited number of options at a time as to what you can pay attention to.
Victory cards/curses take up space in your hand because they're mandatory expenditures of your time/attention. (This isn't great thematically, but it's the best I can do to explain why green cards would show up in your hand even though they're kind of static things.) They could be said to represent how happy your dominion is. (Since land itself is a kind of investment/capital, saying victory cards represent land is a little confusing and doesn't have a good econ analog.)
Action cards represents some mix of capital and technological capacity. They basically represent economic functions whereby you convert time/labor/money/other capital into something else. Each one in your hand represents an option that has been presented to you in the period of time represented by your turn. You can only play one because it requires your labor to operate it. (You're a micromanager.)
Treasure cards, as you've already said, make the most sense not as literal money, but as the dividends of an investment, the investment being some sort of mine. You can play as many of them as you like in a turn because, unlike actions, they don't really require your labor, just your "okay" to produce money. (Again, weak thematically, but keeps my system coherent.)
The operations that are performed by actions (and sometimes treasures) could be explained in econ terms, too, to an extent:
+coin is, of course, monetary output.
Each action can represent one use of your labor. With +actions from villages, etc., your labor can be more effectively used so that you can exercise multiple economic activities in a single turn. (This even kinda sorta works thematically, insofar as Villages can be seen as self-sustaining and promoting economic activity and multiplying the effects of your labor or something.) Cards that offer +1 action don't take any effort on your part to manage or make productive, so you can have them do their thing then you continue on to do something else.
Buys are the most technical and pretty much have the least real-world connection. You could see 1 buy as "the economic infrastructure necessary to facilitate your investment in a single project". It doesn't really translate intuitively to real life because, in real life, investing in things normally takes up very little effort/existing infrastructure.
+X cards represents the generic spur to further economic activity and general foment of infrastructure, etc. This is abstract but seems to cover this case well enough, especially given how many different cards you can draw from this. I can't think of anything else that works in this system. Thematically, it means that your society is moving forward and economically developing faster, so you have more potential options as to how to spend your time/effort/money/etc. and more money to spend.
"Trashing" in this system would mean you're divesting yourself of something, probably by selling it; you can't do this to coppers and estates early in the game because nobody wants to take responsibility for them, I guess.
Hope this helps...
