Radiant Barrier I work in them hot attics all summer long the Spray works and seems to be affordable but the coolest attic I ever worked in was foamed with vents from eve to ridge vent bu what do I know I just do AC lol... Now Duct work, If it is 30 years old you should replace it when you replace your system and most people dont due to costs. If you think about it you are putting a new system and need new duct work designed for that system to work as efficiently as it should. With the new Variable speed indoor blowers you get better humidity control you can even drop down a 1/2 ton in some cases saving around 500 bucks or so .