>>Not just the cost of visual studio, but the time to recompile, test, distribute and fix any problems encountered.
>
>I've upgraded half-a-dozen or so projects from VS2010/.NET4.0 to 4.5 on VS2012 and can't remember any problems at all. Can't say whether going to VSE2012 would be equally straightforward tho.....

One major problem is that I don't think MM.NET has been updated to 4.5 yet, but I may be wrong.