shen - I agree with hedgefunder.
There are a lot of good people who advocate the "dual game" approach so you have --as much as possible-- basically one game that you use gi & no gi.
I asked a very experienced BJJ Professor about this thinking he would agree, but he said the exact opposite. He said if you want a good gi game you have to exploit the gi and use it. You don't want to ignore the lapels and all that stuff. Gi & no gi are differnt and require different tactics to operate at the highest levels.
I personally, prefer the "dual game" (one game for both gi & no gi), because I am a simpleton, but at a higher level of sport BJJ, I think there is truth to what he said. IF you are basically sub wrestling in a gi and not using those gi handles, you are at somewhat of a disadvantage.
I also agree with Luke; I like to make my game even smaller by just using things that are usful in a fight context. The older I get the less interest I have in any jiu jitsu that can't be used in a fight. It's fine for others, I am just no longer interested in it for me.
I think MG mentioned something like "why would I wanna learn two different games and play them 50% of the time, when I can learn one, change some grips but play the same core stuff 100% of the time". Kinda makes sense.
I guess it all depends what you wanna get out of it. If you wanna compete I suppose you want some strong stuff, if you wanna teach its most likely better to know it all, if you're a hobbiest you can likely do whatever