Yeah, personally, I think gameshape is the most important out of the different variables. Along with enthusiasm and homecourt advantage, it seems to raise each players skills and game rating quite a bit. It's also the hardest to keep at good levels, so I would imagine its worth more then enth/hca. It seems to really effect the players game rating, which for me is a players most important stat.
For example, Cody Pearsons first games with me last season, he had average gameshape as I purchased him from a deleted bot team. His shooting percentage was terrible, and only had a gamerating of around 8. After a few weeks, I got his gameshape hovering around strong-proficient, and his game ratings jumped to around 12-13. Then the start of this season, when back at respectable, his game ratings were around 9-10.