Post formatting problems are common with imports because different forum applications use different markup. Often times you just have to live with it. vB and xF use similar markup such that it isn't much of a problem, but IPB is different.
I have seen that problem with quote tags before. That is an example of different markup being used by the source forum. Unfortunately I don't know of any easy way to fix the quotes because of the excess random stuff inside of the tag. Without the random stuff you could do a string replacement query on the post text to replace the tag.
The excess spacing is interesting. I don't recall seeing that problem before. But like I said, post formatting problems are common when moving between forum applications. If there was a direct IPB importer then the devs could probably take a look. But the problem becomes difficult to work with in the context of a double import.
I like Blandt's suggestion of examining the results of the import in vB. That would at least help you to isolate where the problem starts.
