i might add an increasing price mechanic, or maybe flavor it a little different, say "igniting spark" and remove the +1 from the X. i still see this getting broken with some ruby medallions, some familiars, and some dual lands. then it's lightning bolts and mountains all over again. make the first one useless and it might just be the slow down it needs.
I really don't want to make the first one useless. The setup required to make it ridiculous seems like more trouble than it's worth. Let's playtest it and find out if it works as printed.