I brought this up briefly on another forum where it rudely got shot down (with blank ammunition), but I've been researching ceramic microspheres as an additive to paint, so I'll put in my 2 cents worth since you're talking about roof coatings a little bit.
3m makes a whole series of ceramic microspheres that have low thermal conductivity. For $9.75 you can buy enough for 5 gallons of paint- virtually any paint- and come up with a superior coating for your roof. It improves flow characteristics of paint. It increases the R value as an insulator, it increases reflectivity (it's one of the components added to reflective paint), it increases bouyancy (in case you find yourself not only stuck in the sand but floating out to sea), and if you happen to sink won't be crushed until about 4500 feet underwater
Have I used it? No, but I'm buying some tomorrow. When I look at different companies touting the superiority of their insulating product, they all start sounding the same- they all use ceramic microspheres. I saw on "This Old House" they were talking it up as an additive to flat paint because it makes it possible to scrub. I guess normal flat paint you can't clean like that.
Supposedly it wouldn't change the drying time or method of application, etc. of your Imron.
Anyway, I'm off my soap box...