My copy of Lost Cities was on loaner and I wanted to show a friend how to play so I bought two decks of Bicycle cards and marked one of the heart suits with an X thus giving me 5 suits to play with. Although my friend liked the mechanics he commented that it felt dry. Later when we played with the actual game cards he said he thought it was fantastic. So the art and theme definitely made the difference here.
Just wanted to mention that I thought your "experiment" was really interesting. The results made a lot of sense to me too. The game as a whole is worth every penny because it just adds that extra something.