What gargoyle and earth troll?
I tried Sharpen a bit; it can give a nice damage bonus to certain types of weapons, but also adds an agility requirement (ie save before using it).
I didn't learn Armour Usage or Arrow Proficiency. I did learn the Convert Arrow skill for Power Arrows, near the end of the game, but I think I found or bought all the power arrows I actually used. Playing again I wouldn't keep using normal arrows for so long, so the convert skill might be more useful (but it should be pretty easy to build up a decent supply of arrows from loot, or bought in the BF, if need be).
I really didn't learn that many skills, weapon expertise and the healing spell for both characters, my hero learned Identify Equipment, and my DK learned Sharpen and Repair. Almost at the end of the game I found some holy water for sale in the BF, so learned Alchemy so I could make some permanent agility potions for my hero (who had recently found a very nice bow, so switched to that rather than a crossbow). There were lots of spells I could have tried, and I saved trap material to eventually try out traps, but never got around to it (though it was a good thing I saved alchemy plants).
Lockpick would probably be useful (the skill was broken when I played through the disk version, so the only things locked were those with a key or lever to open).