If you shoot HDV at 720p24 your file sizes will actually be slighlty smaller than DV so file size shouldn’t be a deterent. The main thing is to have fast processors to edit HDV.
I just think that if you really intend to finish in 24p you should shoot in 24p. Converting 60i to 24p produces strange artifacting in my experience with Magic Bullet. It can be done but you really need to shoot carefully, knowing what works and what doesn’t.
Anyway, when you say that you were expecting better looking video at 24p SD what was the problem? The motion quality or the image quality? Personally I have not used the camera to shoot SD yet so I can’t really draw any conclusions or give much advice there. It’s pretty comon knowledge that even if your final delivery is SD- it is better to shoot and edit in HD, then encode a standard def DVD or convert to whatever SD format you need if you are outputting to tape.
Hope this helps.