Maxing out

I am up to using a 35 pound plate when doing hyperextensions. I do three sets of 12. I am thinking that is all I want to do. I also think I am doing all I want for my abs. I still want to keep going up on squats, dead lifts, arm, chest and back exercises, but there are some excercises that I just want to be adequately strong to do. By that I mean get them strong enough to support me in my other excercises. Am I off on this kind of thinking? Are there other exercises that you all look at the same way?