Probably would, but more importantly it'll help lower your heating bills. You can do it two ways if the existing insulation is fiberglass bats: lay new bats perpendicular and on top of the existing ones, or blown-in cellulose insulation on top. I prefer the cellulose cuz it'll get into the nooks and crannies. If you have blown-in already, just pile on some more. In our part of the good ol' US I'm pretty sure we should have an R-value of 45 in the attic. I don't think six inches yields R-45. If you want to go all out, seal all the holes in the attic where Romex is pulled through, DWV pipes pass through, and where the drywall meets the top plate of your walls with expandable foam. If you have a chimney you can plug that too, but you have to use regular fiberglass batts and stuff it in the crack with something like a paint stick. Have fun.