Susan,
I have to agree for D3 players that summer ball is very important if they hope to move on. If they are a pitcher it shows they can get other prospects out. If they are position players it shows they can hit with the big boys.
For players that are already prospects though, I can see what the article is saying. If you already on the radar, then this is a viable alternative.
But would a D3 pitcher benefit from for going the summer and get stronger if it would mean it would help get his velocity up to the magic number (90)?