Achievements are fairly important to me, but not so much that I focus solely on getting the max gamerscore for every game. There are a few that I've 1000G'd and even beyond (DLC), but they were games that were worth the time and effort I put into them.
Recently I logged about 350 hours into Blue Dragon, but ended up with only about half of the achievements. I'll admit, I was a little sour about it, but I was not about to new game+ it and log another couple hundred hours into it just to get the rest of the achievements... It was a good game, but meh.
It's also pretty telling that I've never played that Avatar game for an easy 1000G.