I like the idea, but only after three concerns are addressed:
1). Selling. Towers would need to cost significantly less than they are now if upgrading them costs 33% less electrum. I know there's no economy in Elements, but I would feel weird if you upgrade a Tower and sell it back for a net gain in electrum. O_o
2). Pendulum upgrades - I say that if you're going to upgrade towers for 1k electrum, pendulums should get the same treatment. After all - both of them are almost identical in function (generating quanta permanents), which would make it easier for newbies and pro's alike to get semi-upped decks involving pendulums/towers of a certain element.
3). Other costs: Seeing that there's practically no other thing to spend electrum on besides cards, upping cards, and facing opponents, I hope that if some sort of patch was implemented that lowered the cost of cards (themselves or just pillar upgrades), that veterans and newbies alike would also find something to spend their money on, as some people (*looks at jmizzle7*) might have quite a surplus of money that they wouldn't be able to use for the game...