I haven't seen the BV5 HD in a while and not next to BV7 but I believe there is a significant difference.
Its not just PQ, it is also connections. The BV5 doesn't have HDMI which you need for many add on's. Personally I mostly watch DVD and some Apple TV. I would probably be fine with it. If you have HD cable box, blue ray player, PS3, and so on the BV5 may not be right for you.
And it still is significant money
Cheers
JK
BS9000, BS2300, BC2, BL2500, BL3, Bl2, BS1, BV8, BC4, A8