I actually think you're on the right path looking for new speakers given the improvements you're looking for. Read the review below, and in the comparison section the Thiels were better in imaging, soundstaging, and midrange detail (albeit at the cost of sounding relatively thin). Point is, when directly compared in the same system it becomes apparent there are speakers that are better than the VAs in precisely those areas you're looking to improve upon -- not that the VA's are bad at all in these areas, just not as strong as some others. I'd expect the speakers I recommended earlier (along with several others listed above) would show similar improvements while avoiding the thinness and relative lack of bass of the Thiels. And I also think your amp and pre are good enough to let those benefits come through (assuming the amp has enough power of course) although I'd eventually look to upgrade them too. Anyway, hope this helps and best of luck whichever way you go.
http://www.soundstagehifi.com/index.php/component/content/article?id=308:%3Cb
