As I promised, I would report back once I had put this in action.
Well, I tried this out last game and it worked very well... having them done at the same time as saves made them easy to remember, and my mehod of putting a die next to the monster entry on my encounter sheet worked very well. Additionally, I was happy with the way I described the recharge mechanic - I used spriggan giantsouls, and described them as having "an aura of largeness" that diminished when they used the power, and which came back when it recharged (well, had it recharged, really).
How well it worked dramatically, on the other hand... hard to tell, given my inability to recharge the 4+ power on either giantsoul, and given the powers themselves weren't particularly exiting or cinematic (basically, it gives them reach 2 - though, admittedly, I'm not very good at making the best of monsters extended reach). Additionally, given my inability to recharge the powers, I couldn't see if making the recharge mechanic visible affected either PC or monster strategy.
Anyway, so far, so good. I can see it may become a bother with monsters with several recharge powers (especially if I have more than one such monster), but for the time being I'm going to continue trying this out.