Some practical TEC questions

I'm thinking of adding a TEC to my CPU water loop. From reading around the subject, my understanding is that a TEC will triple the load on my WC loop, but drop my CPU temps. I have no problem with my water temps rising another 10-15C. The extra air/water dT should let my rad dissipate the extra heat.

I have no interest in dropping the CPU below ambient - just in reducing the temps to give me a little more O/C headroom. I'm wondering if it might be possible to avoid dropping the CPU temps too low at idle, by controlling the voltage to the TEC, based on CPU temps. e.g., as the CPU temp increases under load, the TEC voltage is increased to keep the CPU within safe limits, while (conversely) as the CPU temp decreases at idle, the TEC voltage could be reduced to keep the CPU above ambient/dew point.

Is this feasible? Has anyone done it?

It's possible, but you need an automatic controller capable of handling a 300-400w tec.
Those are few and far between, as far as i know you would need to build one yourself.