There are tons of collection quests. Most involve important quest chains too, like for example the one in Dragonblight that leads to Alexstrazsa and "the movie" involves at least 10 collection quests. My team is 73, I've done 70 quests in Howling Fjord, 70 in Dragonblight, and 20 in Borean (also cleared UTK, Nexus, and both Azjol instances) and I'd guess at least 30-40% of the quests I've done are collection quests.
Most are really not too bad, usually 5-6 items from mobs that drop 100% (but one at a time). There are a few however that are maddening, like the ancestor-bones one in Howling Fjord -- you have to collect 5 bones from mobs that are camped constantly and spawn rarely, and the drop rate is close to 30%.
When I level my DK team I am skipping ALL collection quests, they are just too frustrating. The only ones to do are in dragonblight, get every quest done in that zone since there is a fairly significant story line that opens up when you do.
Re: the XP issue, I think I've noticed that as well, although I've only multiboxed. Its very frustrating that my team is only level 73, whereas I see people who play as much as me already 76 or 77. Oh well, I'll be able to solo heroics hopefully at least :)