I've got all but V8 on one machine and V7 and V8 on another. Never had a conflict problem. We did notice something a little odd last night but certainly nothing like what you're seeing so no, leave them there. I oftenly use the older versions unless I need the features in the later versions as they do seem less resource hungry.
Don't ditch Vegas 6.0d yet! In about 5 weeks of heavy use I have found 3 bugs and several annoyances regarding Vegas 8.0a, some of which actually appeared with Vegas 7. Vegas 8 is NOT rock solid, smooth, and quick like Vegas 6.0d. Wait until Sony addresses all the issues with this new release. And if they don't? I always evaluate ALL manufacturers' software for possible deployment. That's how I found Vegas in the first place!
>>>For example - you can capture 24f Canon XH-A1<<
I've read the same thing about Canon HV20, but I just plug in and capture 24pf with or without scene detection. Both ways it works fine.
Others said they were getting a new scene for each frame ending up with hundreds of clips ( in V8 ). Are we talking about the same thing? Because I have no problems whatsoever. And if Sony's support is seeing the same thing I am, there is no problem to see.