Of course I have, I'm looking at it from the perspective of an executive or lay person. Arguably the flash is more popular than green lantern, so why did they go with GL first? Probably because it provided a better marketing potential with the ring and toys.
Sometimes you guys need to look at these things from an objective perspective.
I think Flash has pretty good marketing potential. As a character, hes often the funny wise cracker in the Justice League and that could be aimed at older children and if they develop his character properly he could definitely pull in an older demographic. On top of that, the potential for awesome action scenes are astronomical. A movie would sell itself.
As far as other marketing streams go you can sell toys of things that never actually appear in the movie. Toy guns, vehicles and action figures (not to mention Flash masks and gauntlets). Is it stupid for the Flash to have a car? Absolutely, but if you make it look like a pimped out Ferrari and toss some Flash logos on it, kids will eat it up. Kids are great.
You could also market the crap out of the villain. Captain Cold Ice Cream/Ice Pops, Mirror Master holographic Happy Meal cards and toys, etc,
As long as the movie is awesome (and can make the Flash look cool) then you could easily throw a Flash symbol on anything and it could sell. Backpacks, shoes (that could be a cool one: 'Hey kids! These shoes can make you as fast as the flash!'), notebooks, clothes, video games, etc. You just need a good director and producer with some solid actors and good plot.