"I'm relatively new to Everquest but very familiar to MMO's."
Welcome! Great to see a new face.
"For starters, I've been reading recent posts on these forums that seem to carry a negative opinion about monster missions"
People are rather cynical about EQ now.. almost all aspects of it. Its just the general view.
"Do people still do them for fun or is it just for exp?"
You're right to put these two points together. The cynical nature comes from the answer to this.. its for EXP. Doing the missions over and over and over isn't fun. EQ is about escaping from real life, not about fun.. takes a while to realize it, I guess.
"Secondly, I've seen the Shroud folks in PoK, but I've not seen anyone there that assigns the actual monster missions. Where abouts would I find the NPCs that start these quests?"
Those Shroud folk in PoK are for if you want to become a monster, and then, otherwise, play the game normally. You'll have to go to specific locations to do missions.. and you need not be in any form when you go to them. Just check around the site for this sort of information.
"Can I really do these missions with other people even though I'm still a low level toon?"
Yup. When you start a mission, it butchers all skills and abilities a player once had, and they don the new avatar. A level 1 can be far more helpful an ally than a level 70 in a MM, all depending on the player himself. Group Leadership abilities and points are the one exception to this.
"is it worth my time to level up more and explore the content of LDoN first"
LDoN's, unlike MM's, do not grant a new avatar to the player. LDoN groups tend to yield less experience and are a bit more old fashion now, so they're not nearly as popular as they used to be. I'd suggest doing a couple, starting in your mid-20's or 30's. If nothing else, they give you a truer feel for the game.. MM's, though very helpful, are very.. skewed.
"level grinding more appropriate until I can be more effective to a group? "
As long as you're a decent player, and there are no outstanding flaws to your character, you should always be an effective addition to a group of your peers. However, finding such a group may be difficult now, as much are in the extreme end of level ranges.
Just.. a personal note. Many are almost unspeakably wealthy.. some are even generous with a small percentage of their fortunes. If you accept such gifts, it'll help you advance much more quickly, but it may loss a bit of the "real" feeling and jade you.