I find not having a front mudguard gets my feet wet more then anything. Never really had a problem with sprey in my face unless i have been riding close to someone infront going down a wet muddy road. Even then they had full mudguards and the flappy bit at the back to stop sprey.
However, i forgot to put my mudguard on the bike on Tuesday and i rode down to the caravan (about 7miles) in the rain, with alot of standing water and i dont have any stains on the back of my trousers or coat. The bike did get alot or road dirt on, most being under the saddle and on the saddle bag. I was on main roads aswell so i was getting alot of sprey from cars and trucks.
So, besides getting wetter, having a wet-ish arse i didnt have any road crap marks on me.
So Bonj is slightly right, but if you do want to keep a dry arse then mudguards are better then none.