The highest tier is 15000 and I just got over 8000 in a single game. Judging by the high score table that's far from rare.

That's actually not a bad idea. I usually score in the 3-5k range for that game and I'm sure lots of people are better at it than I am xD I'm pretty sure that was among my first achievements.

When the game was released heaps of people complained that it actually makes them dizzy.

It personally makes me so dizzy that i can't even sit straight on my chair anymore after playing the game. So I wouldn't really be a fan of upping the achievement :s