The house is around 3k sq ft. I have maybe 14 x10 devices- none of them 2-way.
I am using a leviton repeater/active phase coupler.
A 3k sq ft house is a good candidate for a coupler/repeater but since you already have one, that should be sufficient.
So what do you think? Shouldn't this Leviton boost the signal more??
I would have thought it should be doing a better job. It could be defective like Brian said.
Is there a SUPER POWER repeater out there?
I believe that the ACT CRs drive at 10V instead of the usual 6V. I don't know for sure what voltage the Leviton drives at but it might be worth looking into.
What do you do if you simply have too much signal absorption going on?
First I would make sure you using noise filters on the most common signal absorbing devices (UPSes, powerbars, etc).
Also do you have any Arc Fault Circuit Interrupters (AFCIs) or Ground Fault Circuit Interrupters (GFCIs) in your breaker panel? They have been known to attenuate the X10 signal and being at the breaker panel, they could be dragging down the whole house.
As a last resort you could try using some signal amplifiers (such as SmartHome's BoosterLinc) on circuits that are particularly problematic. Just make sure they aren't too close (electrically) to any powerline transmitters since they can actually weaken strong signals.