less piracy should in theory result in less viruses spread around PCs. Also with more people actually buying stuff in theory prices should go down but i really doubt this one
Torrent sites getting shut down doesn't reduce copyright infringement, and software copyright infringement is a tiny part of the whole. Most people are trading TV and movies, and running an exe from an unreliable source is very foolish.
Prices aren't generally impacted by copyright infringement at all. Businesses charge as much as they think they can get away with. If anything if the torrent sites all disappeared along with the other sources that shall not be named, prices would go up because the competition would be gone.
The way to reduce infringement is to lower prices to the point where people think they're reasonable, but it may be too late now that we've trained a generation to torrent media.