So do attachments like Resourceful count as card effect?

Yes.

I'm curious though, how are you pairing up Resourceful and Heir of Mardil? The only thing I can think of is: a hero is exhausted after the Refresh phase. Maybe you used Denethor's ability, for example, or they have a Condition on them like Caught in a Web. Is that what you're doing?

i am new so i couldn't remember the name of steward of gondor so that is why i asked for the first attachment that gave you gold that came to mind hahaha. But I also play denethor so this is something i would do as well.