1) How useful/necessary are Robes of Resistance?
For the most part, not very (IMO). Some of them give you a snazzy new graphic though. 
Largely, I didn't notice many enemies using elemental spells that harmed my mages. Doc gave you some neat "outside of the box" uses for them, though.
2) Is a Robe of the Archmage really worth 16K to a fighter/mage?
You can't cast spells wearing armor. Archmage Robe gives better AC, some bonuses, and you can cast spells wearing it. What's not to like?
Besides, you got anything better to spend that 16k on?
3) What is the range/sensitivity on "Detect Evil"? It seems to vary. I have Ajantis use his special ability occasionally. Sometimes, he detects evil chars way off in the sector, other times he reports nothing when there is a group of inimical monsters fairly close.
I'm not sure. In BG2 the range seems nerfed in a BIG way, but in BG1 Ajantis was usually detecting the entire map for me. Could it be that the enemies Ajantis detected weren't evil, but neutral?
4) There are several instances in the manual referring to a seemingly generic "Hit Dice," e.g., in some spell descriptions ("the wizard conjures 8 Hit Dice of monsters" & "monsters with 4 +3 Hit Dice or more are unaffected"). What does this mean?
I'm not an AD&D guru. So these are just guesses.
I *think* it refers to how many dice you'd roll to determine the monsters' HPs in tabletop. Certain monsters you might roll 1 dice, others you might roll 8. So if "Wizard conjures 8 Hit Dice of monsters," he could get up to 8 puny monsters (1 hit dice each), maybe 2 4HD monsters, 4 2HD monsters, and so on. It'd probably specify the maximum number of Hit Dice it can spawn on a single monster as well.
"4+3 Hit Dice" might specify a monster which has 4HD but for each HD it's given 3 HPs (or perhaps 3 is added to the total after rolling 4 Hit Dice?), which would make it a bit tougher than a generic 4HD monster.
Again, I'm talking out of my league here and very likely have no idea what I'm talking about.
5) is a wolf a good addition to a team? It wouldn't seem that good in combat - maybe as a scout?
Doc answered the first part, so I'll take a stab at this. I never found much use for the cloak. On decent fighters it makes them into a weakling little canine. It *might* have applications on mages or thieves if you really, really need an extra hit per round. (I think Wolf has 2 hits/round.) But I always preferred my characters in their natural state. (Side note, I also wasn't fond of Polymorph Self.)
6) In some cases, an enchanted armor (e.g., Chainmail +2) will give the same AC as a heavier plain armor, thus saving weight, allowing the char to carry more stuff. However, using the enchanted armor won't allow using a item of protection +1 with it. If I understand how things work, I would think that overall, the +1 to saving throws would be more valuable than the increased carrying capacity. Comments - agree/disagree?
It's hard to image being so space-needy that I'd give up saving throws for less encumbrance.
7) How often do you run into skeleton warriors? One guide I've seen calls them one of the most potent monsters in the game (worth 4000 XP). Is it worth giving chars proficiency or specialization in blunt weapons or missile weapons to have a counter for skel warriors, or aren't they worth worrying about?
Skeleton Warriors are fairly rare. They pop up more frequently in Durlag's Tower than anywhere else. (Only place I remember seeing them outside of Durlag's is en route to the end area.) They *are* badasses, but you probably don't need to go out of your way to defeat them. Even so, I usually have my mages specialized in missiles. Hurts less than meleeing!
[o: *LEMMING* :o]