what was the sweatbox?
Pretty much as the other posters have said. It was a box with painted sides, can't remember exactly but I think they'd chuck a ball in, the player would then have to control and hit an assigned part of the box. Helped with improving speed of thought and didn't intrude on main sessions. Edit: also think the early version Shanks had was essentially a giant sandpit as well, probably just to make the players sweat that little bit more; from digging a bit deeper, and coming across an old thread on RAWK
http://www.redandwhitekop.com/forum/index.php?topic=305389.0 it sounds like Shankly had two back in the day.
At Dortmund, and I believe they still use it (as well as Hoffenheim now), Klopp introduced the Footbonaut system. At the time it cost a couple of mil to install, might be a bit cheaper now, but it does mean players can have individual skill lessons after their main sessions are over. Obviously because Melwood was so small I'm not sure we could have had such a machine but with the expansion maybe it's a possibility.
Personally I think it would be worthwhile as klopp would be able to get players doing skill focused session after training and anything that could help the coaches would be more than welcome to be honest.