That sounds like an interesting idea. Give it a shot. Tell your players its a temporary thing while you test it out, and see what happens.
If you like that idea, you might also look at the Savage Worlds Adventure Cards. They make a set for D20. I used them for D20 before converting to Savage Worlds as my primary RPG.
As a side note, when my players started getting slow in D20 combat (well, slower than usual), I'd just start a count down, usually from 10 (in as non-parental a way as possible). If I got to the end of the countdown without a declared action, they were considered to have "frozen up" that round. Net effect: they sped up.
