Scotch guard on hiking clothes ?

I don't see any reason why it'd help with drying time on your wool socks. Might prevent them wetting out for a little longer if you were to wear those wool socks as outerwear during a light rain, perhaps as rain mitts.

Scotch guard may reduce breath-ability of materials where you want breathability, like socks and fleece.

My own experience with Scotchguard:

1. It does not affect breathability
2. It gets overwhelmed pretty quickly – after a half-hour or so of brushing my pant legs against wet grass, Scotchguard makes no difference.

For me, I wouldn't bother with spraying just to give myself 20-30 minutes of rain repellence. Don't need it really on short day trips. And pretty useless on multi-day trips.

Scotchguard is good though for protecting neckties from business luncheon spills/mishaps — allows for quick wipe up's.

I have been using Camp Dry on my nylon hiking pants for that same purpose. It's something like a 13% silicone solution spray. It works great for hiking through wet brush and such, and I haven't noticed a decrease in breathability. It really helps to bead water up, but if you put any pressure one it (kneeling, sitting on wet stuff etc.), water will be forced through.

Order Revivex from REI. Tectron good but Revivex is the "Gold Standard" of DRW treatments. Buy 2 spray bottles. It's that good.