I rephrase "Do flash comics sell?".
With the right creative team, I think they can. Take a look at the Green Lantern line. It is selling fantastically right now thanks to Johns, Van Sciver, and Reis.
Relaunching the Flash like they did with Green Lantern. DC should be putting heavy focus on the Flash IMO because he has a lot of potential.
With Barry back, I think DC should put Flash back into it's original numbering to issue #600+ (350 issues with the first volume, currently 241 issues with the current volume, and the 13 issues of the third volume). Have a high profile team that can deliver the excitement.
Resurect Bart, but deaged and back as Kid Flash and on the Teen Titans.
Find a cure for the West kids and have them a part of a reformed Young Justice.
Have Wally on the Titans and Justice League of America.
Have Barry on Robinson's Justice League with Hal and Ollie.
Obviously have Jay on the Justice Society.
Meanwhile in Keystone City and Central City you have a team of superheroes patrolling the streets just like in Gotham City and Star City. But unlike Batman's team and Green Arrow's team where Batman and Green Arrow are the obvious leaders of their tight knit group, they're all equals.
That's how I'd give the Flash a relaunch and make them have a very prominent position in the DCU just like Green Lantern.