I would say 'it depends' with the corpse cart. If you spend 100 pts on it, then to make it worthwhile, you must raise 100pts of units with the load stone (just about, not including bound spell). If it only helps you give ASF to skeletons and raises an extra 5 skeletons through IoN, then it's not worth it. You can do a lot with 100 pts.
It definitely CAN be good, but what makes it good is synergy; how it works with your list.
I personally don't use Necromancers often. I think the extra points spent on a vampire are well worth it. In certain lists to use as a scroll caddy if you're magic light (zombie dragon) or a powerstone holding VHD to ensure certain units make it into combat are the only things I use them for (what MasterSpark said). Other than that, they can't go into combat very well, which means either a unit to baby sit them, or accepting they will die. I personally think a vampire with a decent armour save is the better buy 90% of the time.
I think 60% or more of people prefer ghouls over skeletons; I am not one of them (I loved 6th ed. skirmishing ghouls, but prefer skeletons with standards more; its a style thing). Stats wise I think ghouls are better, especially against a lot of units out there. Now I'm assuming you don't have 200 ghouls; if so, I'd say buy something else.
Put some context to your posts! List your army, what you like, and people would be better able to help you.