I'm doing a mod right now that "could" do wattage control if I wanted since I'm going to employ a fairly accurate current sensor with it. However, I'm still going to use voltage control. The current sensor will only be for user feedback, not control. I've actually wanted a current sensor since the first mod I did, but I only recently came across a way to employ one for high currents cheaply by using a 10mm length of 16ga nichrome wire. High wattage current sense resistors are large and expensive. Though I'm going to have to figure out how to solder that stuff on a PCB.
Voltage control just seems like the best way to me. One downside with wattage control is the reliance on two control points instead of one. The error for voltage control is going to multiply with the error for current sensing. So, for example, if your voltage control has 2% error and your current detection has 3% error, your output will have 6% error by wattage control and 2% error by voltage control. Really not a big deal since you probably wouldn't notice a 6% error anyway, but as a matter of design principle, voltage control is going to be more accurate. However, as already stated, that's getting into a "lipstick on the pig" kind of thing.