I have not used waterproof socks so far, but have considered them and talked to a few people about it.
For both of my
Camino Frances, i followed the strategy, that in May/June when i was on the way, the risk of rain was there, but the risk of continued strong rain was limited and the risk of heat was greater. (yeah, one year its this, next is that, but in a general, statistical way...). Hence i went for light rain protection and equipment suited for warm climates, especially trail runners with lots of holes and no waterproofing whatsoever. The theory was, that i could always just sit out a day or two if weather turned seriously bad or buy missing stuff in one of the many shops. Luckily, this was not necessary since i had little rain. Walking half a day in wet-ish shoes is one thing, walking days in soaking wet shoes is something different.
So in conclusion, it worked really well and i would do exactly the same the next time on the CF.
On the other hand, i still have this idea, to walk the ~3000km from my doorstep to Santiago one day. This would change things a bit, and I likely would start somewhere around March or April in Germany where the weather can still be rather unpleasant for days (or not...). Since i am really fond of my trailrunners, i might chose to walk with them and now... this is where a pair of waterproof socks might come in handy as a "security net".
Well, that's my thoughts on that, hope it helps you make up your mind about it a little.