Invisibility on a large battle mat, where 5' accuracy matters, is a nightmare.
I think the easiest way to make Greater Invis. less ridiculous is to limit players to in character information. Someone already suggested removing the invisible offender from the battle mat. Go one step further: Make them tell you in secret where they going/what they are doing. If they inform the other players where they are, equate that to them drawing attention to them selves, and allow the enemy to pinpoint them as well. (unless they use some special means to keep such information secret) When the fighter tramples them during a well-planned charge, or the wizard barbecues them with a fireball, they might start thinking about limiting their use of the spell.