Unless the text values are bugged on the cards, upgrading to ++ is basically never worth it. A good example is the work hard card. Work Hard is 10 Energy for 3 Work, + is 5 for 3, ++ is 15 for 10. However, with the Work Ethic card, Work Hard gives an additional +2. This means that for 15 energy with the use of Work Hard+ you generate more Work per Energy than you would with the Work Hard++ and Work Ethic++. This is the same for basically every card in the game - the cost always becomes more expensive than the value of the card.