Well, this is one of those things that likely doesn't have a right answer. It will reflect values that really must vary from family to family (for example, I rarely watch TV and think it is a huge yawn, DH watches TV, but doesn't understand why I like to game).
My DS9 loves computer games. He likes Wizard101, LOTRO (he only gets to play that when I play with him), Civilization and various military strategy games (Rome total war - graphic violence is not allowed). Like your boys, he does great in school, plays violin, does sports, lots of playdates, etc.
My kids have always been given 30 minutes a day of "screen time" during the week, and an hour on the weekend. When he was younger "all" computer use counted, including playing educational games. We started to get some serious push back on that as he needed the computer more for school (which was reasonable), so what we did was tell him he could use the computer more, but it had to be semi-educational (Scratch, or programming Mindstorms, Gizmos, Brain Pop, etc). So, for pure games, he gets the 30/60 rule, but he can use the computer more at other times (with permission) for other projects. When it comes to time limits for the other stuff we stay flexible, if he is just roaming the lego site looking at things he wants to buy, I'll cut him off, if he is designing something cool on Scratch, I let him keep going (within reason of course).
It sounds like part of your concern is that he isn't investing time in other intellectual interests. Maybe getting him into Scratch or Mindstorms or something like that (if he isn't already) could be a way to combine interests and make you both happy.
