People who play games solely for Gamerscore are apes. There is no point to waste time just for Gamerpoints. That being said, it is respectable to have Gamerscore for the games that you play and devote time to.
I value having a high Gamerscore per game, and achievements, rather than having a high Gamerscore overall. Any ape can get Gamerscore for Cars, Avatar, and other games that require no skill. On the contrary, it makes your gamertag a little more reputable if you have high Gamerscore for games that actually require skill.
The way I see it is that no one can see your in game rank outside of the game itself; but through your Gamercard, they get an idea. 1000 Gamerscore for a game generally denotes skill at said game.
I'm putting a lot of thought into this... hopefully some of you will understand my viewpoint. For example, (to illustrate my point), you probably don't know that I have 21,000+ kills in Gears; however, you can see that I have the full 1250 points. You may not know that I was a Top 100 racer in Burnout, or have a Trueskill of 21 in Forza and was formerly ranked in the Top 1000 for Time Trials; however, you CAN see that I have the full Gamerscore for both of those games. You most likely don't know that I am a Colonel Grade 2 in Halo 3, but you can see that I have the full Gamerscore for that game. And you definitely don't know that I'm on my second Prestige mode in COD4 with 13,000 kills and a 1.44 k/d ratio, and am also ranked #10 gloabally for Mile High Club and #70 for All Ghillied Up, but you can see that I have the full Gamerscore, which denotes skill at the game (Mile High Club on Veteran is ridiculous!).
So, there is good Gamerscore, and there is bad Gamerscore. The reason it's there on the Gamercard is to help with identity on XBL or something, to let other players know what you play.
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This is the truth that I am revealing before you! Behold; those who hear me now, have got ears to hear from!