Suspension upgrade and breaks

The short answer is yes. With enough money you can do anything.

The long answer is that you can easily lower the car, and swaybars (anti-roll bars) are readily available as well. There are many threads here that discuss it. My car is lowered 1.5in (on stock struts/shocks), 18x8 wheels, and aftermarket rear anti-roll bar, and the Carolla front anti-roll bar. The car corners very well but still needs more negative camber in the front (-1.3 now, I'm going try -2.0 next). The wheels and tires cost me at least 5mpg. My wife gets 45mpg, I get 39mpg.

When it comes to the brakes, I drive the car pretty hard. Very damn hard actually, and I haven't found the need. I thought that brake fade would be just part of the experience of owning a Prius, but I've yet to experience it. I'm sure it is possible, but even on mountain roads I haven't experienced it yet.

In the end, it's a Prius. A better handling Prius, but still a Prius.

 

The brakes under normal use do not use the normal hydraulic disk drum setup "although these are in place" so upgrading the brakes will have no effect until you get to the point where the regen can no longer cope with your braking.
One possibility if the brakes are "upgraded" is that when you get down to 7 mph "the point at witch the hydraulic brakes come into operation "on slippery or loose surfaces" you will lock the wheels as Toyota balanced the transition from regen to hydraulic braking to be as smooth and even as possible.
The other strong possibility is that the VSC "vehicle stability control" that relies on the ability to apply braking on any wheel automatically, in the event of an uncontrolled slide will get you into more trouble. Instead of getting you out of trouble. Operating brakes that are more effective than ECU's are programmed for or expect.

John (Britprius)