Heh, having objectives to focus on that at least change every so often is good. There are some collection quests that even I won't do as a 5-man. (The quillboar tusk one in barrens is one. The T0->T0.5 upgrade quests are another.) Some of them are just so stupidly long and don't lead to a follow-up chain or instance quest that it's just not worth what effectively is a distraction from normal quests. Another example is the Elixir of pain/agony/etc. in hillsbrad. I'll do the first one (for the bear hearts/spider ichor) because the bear hearts are now 100% drop rate and you're already there for the Durnholde quests anyway. I don't do the lion blood because it's just not worth the extra effort as you'll outlevel the zone from the rest of the quests anyway.

As someone above noted, having done the collection quests once or twice gives you a good feel for which ones you can bypass and when.