This is something I think about frequently. If they could remove the "bad" parts of the illness; the parts that make my life hell, but leave the creativity and humor, I'd take the cure. But... I know that some of my creativity comes from the "bad" parts. My PDoc pointed out that so much of my photography is about finding beauty, even though my head is filled with not so beautiful stuff. That I use the photography to bring light into my darkness. And my brother said that I see in photographs. I get engrossed in trying to get the perfect shot. When I got my DSLR, it was like having a limb reattached that I didn't know was missing. So yes, I'm sure that curing the mental illnesses would deeply impact who I am. But then again, it would open up a whole world of new possibilities.
On a broader scale, I wonder what would happen to the world if mental illness was cured. Obviously, arts would take a hit. But so would progress. It takes out-of-the-box thinkers to come up with radically different ways of understanding the world around us, as well as new ways of doing things and new products. I think that people who have mental illnesses are less likely to accept the status quo. Unfortunately, rather than tapping into this potential wellspring of knowledge, we are usually disregarded and relegated to the fringes of society.