Welcome! Lowering your car could have a long pay-back time if you only count the fuel economy benefit, dependeing of course on how much labor you can do for yourself and how expensive any replacement parts are, as well as how much highway driving you do. There was a
good thread about this elsewhere in the forum. Then again, you might want to do it for other reasons, so the FE benefit would be essentially free. Assuming you get decent prices, the other things on your list seem worthwhile.
Another
thread on lowering.