I think using a Johnny joint for the rear, trailing arm is an excellent idea. I did it on plastic fantastic (the first one). Be sure when you install them that you can reach into the joint to lube it. I didn't have that trouble because I was using aftermarket, offset arms - but on a stock arm that could be a bit of a challenge.
On the front, granted it was hooker side pipes, but I never had problems with the poly bushings on the control arms.
I would not do johnny joints on the front - it's a lot of money for flexibility in a direction you don't need. I'm also not a fan on heim for anything but racing because they wear out fairly quickly - and unless you're on checking it on a racing schedule, it's just a catastrophe waiting to happen.
my 2cents - but I am not a pro no matter how much one may squint in my direction.