If I have Knights of the Sun and Starfall both in play, every gold coin on the Knights is worth +2 STR, correct?

Likewise, if I have two copies of Devious intentions on a character, does he get +2 STR for each power on him?

Yep, that's how it works.

Eldil said:

Speaking of the above cards, can you spend that gold? Does it go away at taxation?

No and no, unless stated otherwise.

arcanjl said:

That is what I thought, but other players did not think so - thank you!