I agree about the warped bobbin . . .i have a Babylock Tiara midarm that uses metal bobbins and they occasionally warp. They're apparently not made of the same type metal as my Bernina 350 bobbins because I've never had one of them warp.
As for needle . . .if you have to ask about changing your needle, the answer will always be yes. I doubt it will solve your tension issue, but frequent needle changes is always a good idea. I change the needle on my 780 everytime i put in a new bobbin. On my 350, which uses smaller bobbins, I change the needle every other bobbin.