Reddit mentions of Bon 15-432 18-Inch Wizard Squeegee Drywall Smoother

Don't count on paint to fill in anything.

And don't trust your eyes necessarily to notice what will or will not stand out.

Trust your fingers. If you can feel changes in topography as you drag your fingers across the wall, it will definitely show through your paint.

Intense option on skim-coating is to thin down some all purpose compound and apply it with a roller, then skim it off with a wide trowel.

These guys are kind of gimmicky but I can attest that for an amateur they really help. I found one locally at the Sherwin Williams store. Might have even been cheaper than Amazon.

I guess this could be a viable option, but it seems like a pain to try to find and mark all of your ceiling joists so you're getting screws into something solid. Let alone holding it flush against the ceiling while doing so (unless you also want to rent a drywall hanger).

I know I already mentioned it, but seriously consider skimming it. Worst case scenario, it's terrible and you can go back to your new 1/4 inch veneer plan. But I don't think it's really that hard.

You could even try one of these: https://www.amazon.com/15-432-18-Inch-Trowel-Drywall-Smoother/dp/B008JBQCVS

I would skim over every area that's rough or cracked. You can go back and sand it if you can't get it even with the trowel. Use drywall mudd and thin it down with water to a consistency that works.

http://www.amazon.com/15-432-18-Inch-Trowel-Drywall-Smoother/dp/B008JBQCVS