Yesterday we played our first game and we truly loved it.
The only doubt that we have is that in ages III - IV every time someone got a card previously invested, the investment bonus was so huge (counting the development and visible icons) that the supply emptied after the complete action, resulting as a "free" card for the player.
Are we doing everything alright?
Something seems wrong (I think). You only get the investment if it passes around the table without someone sniping you and you take the card. If you are bidding on a card such a small amount (because the investment makes the purchase a net positive) the other players should be sniping the hell out of you. Sniping is a far better route because you get the card in one action, as opposed to two. This is further beneficial if the pot is dry because the person getting sniped does not get a windfall either (IIRC). It is also not a "free" card in the sense that you paid two actions for it. I would rather snipe two cards for two actions. Only downside is that transfers money to another player.
NB: It has been a while since I played the game, but this is my recollection of the rules.