I've completed the dawnguard main quest and have started doing the odd couple of quests for dawnguard where you hunt out the vampires and stuff like that, through these quests i obtained the dawnguard rune shield and rune hammer which are pretty awesome but after that, is there any point in doing them? or are they just going to be endless quests like the ones for every other guild?

Endless Guild Quests.

Keep doing them, eventually flourtentias( not spelt right) will have another job for you, and another new weapon, I don't know how long this goes on for tho.

They are unlimited so you will never run out of quests.
Sure they are mundane, but it is something to do.

The last weapon I received was the Rune Axe, I did about 7 or so after and stopped.