Is it worth seeking disability accommodations if I get good grades anyway? I have bipolar disorder and take medications that make me foggy and confused.  Because of this I am thinking of asking for extra time on tests.  But I generally score in the upper half of my classes, even when I am taking my medication.  Should I still register with the disability office?

Also, my advisor is teaching the class I'm taking, and many of the TAs are people I already know, who may think I am trying to game the system.

Edit: Also, do you think I should try to get accommodations for my qualifying exams?  Or are those not a thing?
The purpose of disability accommodations are to put students on a fair playing field. If you have a condition and if your physicians, mental health providers, and university disability office feel that it puts you at a relative and unfair disadvantage by making you foggy and confused, requesting accommodations sounds both ethical and wise. The fact that you happen to be a relative high performer in spite of your disability does not mean you are not at a disadvantage relative to your peers in this concrete way that can be accommodated for with extra time (for example).

The reality, of course, is that accommodations are not evenly distributed. In general, socially and economically disadvantaged students will be less likely to be diagnosed and provided with accommodations for their legitimate disabilities. There is also a sense that some people have that students will fabricate or exaggerate disabilities to receive accommodations that would help any student but that do not actually compensate for a legitimate disability. In this final sense, people might think you are trying to game the situation.

It would be wrong to game the situation but it doesn't sound like you are suggesting that. Despite others perception, it is both ethical and in your interests to be accommodated for your legitimate medical disabilities and I would definitely do it.