vapor smoothing of ABS is fine but only gets so far like the flow out of brush applied paint. It depends on how smooth you want the surface. If you intend to make the surface as smooth as say injection molding or to have it metal plated for "say " perfume bottle caps, after vapor smoothing or even spray painting with a primer a process called print through will leave a little of the texture showing and mirror plating will make that horribly visible.

We came across this problem when one of our clients wanted to "gold" plate a batch of 3d printed replica FA Cups. The answer we came up with for was to use a 100% solids primer then sand the result.