I have at least 14 WS467s (or earlier equivalents) and none of them turn on by them themselves ( or at least not often enough for me to have noticed). One of my appliance modules, that controls a flood light at the back of our property, used to come on once in a while from what I believe was the noise from a power company transient that was generated when they switched the load near in our area. This transient was so fast that incandescent bulbs didn't even dim, but you'd be aware of it on a TV or Hi Fi set. Interestingly enough longer transients that produced outage blinks and caused the stove and microwave clock to have to be reset didn't turn this floodlight on. The reason I'm mentioning all this is that it hasn't happened since I installed a whole house surge protector several years ago and I didn't realize it until I was rereading this thread.
I don't know how big your electrical box is or what your skill level is but whole house surge protectors from, say, Home Depot are well under $100 and not that hard to install if you're used to doing electrical work safely. I put ours in after spending over $200 on two different occasions to replace the clock in our kitchen stove after it was wacked by lightning. All our computer and AV equipment came through fine because they're fully protected and we disconnect the computer stuff anyway if there's a storm. Completely aside from your X-10 problem this is something you should seriously consider if you're in an area that is prone to lightning.
