@N0x - Thanks for the link; that's really helpful. More or less exactly what I was looking for - to gather opinions from other players about which skills they feel are best/worst and to open a dialogue about the merits of skills in general. Great post!
@Cavemandiary - Lots of good and relevant points. Absolutely the party makeup and difficulty will change the effectiveness of various skills. That's why I included some information about my own party before I gave my opinions (and for my first run I'm playing Classic difficulty)
To be honest I hadn't even used the respec mirror until after I put up the OP so my experience with playstyles other than my own is scanty at best. That's partly why I wanted to see what skills other players like or dislike - if I know which skills to target/avoid, I can save myself some time testing builds. Just yesterday I changed my INT-based, wand and shield wielding Elven Summoner/Poly support magic character into a STR-based, two-handed sword wielding Warcraft/Poly melee character and my skill priorities changed drastically. With Sebille's Scoundrel build, both my Lone Wolves are now committed to Physical attacks, so physical burst damage skills are elevated because the goal in every fight will be to destroy physical armor and then kill or CC targets. Additionally, low-AP cost skills from 'magic' groups like Hydro, Geo, Aero etc will be more important since I'll want to invest at little as possible in those skill groups and invest more in Warcraft/Scoundrel/STR/FIN/WITS/Dual Wield/2-Handed. Infinite Free Respecs FTW!