1.) Yes, it's all very circumstantial, but there are many situations where grouping with others is less efficient than soloing, duoing, etc, particularly in the low levels. It really boils down to skill of the player, class you or they are playing, gear level of said players, etc into infinity. Since so many players on this server have been here a while, many have money to burn on alts to twink them out, so a large section of the server might never group with anyone until around 20. It's at this point where mob hp and damage starts to force players to work together rather than alone, even if they're well-geared, for mutual benefit.
2.) You can vendor the bat wings, most players aren't going to buy them from you when they can buy them cheaper from a merchant in EC. You want to hang onto bone chips, crushbone belts and pads, high quality hides, bandit sashes, and a few other things I can't think of at the moment. If you're ever in doubt, look up the item on the wiki. If there's not a price listed, it's (normally) okay to vendor. There are some items that people just have never gotten around to adding tunnel prices to (
http://wiki.project1999.com/Frozen_Orb, for example), but generally speaking you're in the clear.
We all started somewhere, so don't feel bad for asking questions, even simple ones. It's community that keeps this game alive, and nobody knows everything. I'm glad you're having fun, sorry for the late response, and I hope to see you running around Norrath. If you ever see me in-game, I've got a spare drum and lute for you if you're still rocking out on the bard. Cheers!