I think the fundamental principle that the cards *will* increase in value is good. It avoids stalemates on certain maps (especially the big ones), and it keeps games interesting.
But what we know is that escalating games almost eventually degenerate to "I need to attack 1 territory" to get a card or various other things where the focus of the game *becomes* the cards.
Why not a card setting that increases the cards more slowly? Rather than 15,20,25, etc. why not, 10,11,12,13?