The directions say "wipe dry immediately." Perhaps the Howards website has additional info explaining why it is applied this way. I assume they have a reason. I suspect that a thick layer may not be as durable as the original finish. Or perhaps the layer will end up blotchy -- shinier in some areas than in others.
I have never tried applying more than one coat. You want to darken the lighter-colored scratches without changing the overall color dramatically. The idea is to blend in the scratches with whatever is already there. If you want to darken the overall finish, I'd recommend doing it the right way, by spraying on colored toning lacquer. These old cabinets were originally finished with lacquer.
Again, I don't have a lot of faith in Howard's and I don't use it regularly. My suspicion is that it's not as permanent as a "real" finish such as lacquer. It seems to be popular with people who want to freshen up a tired finish long enough to resell the piece.
The directions recommend that you follow up by buying another one of their products -- Howards wax -- and applying that. Perhaps you could try this and see if you're happy with the results.
Wax is another thing that I don't use on refinished cabinets. Wax is impermanent and I think it collects dirt over time. A cabinet that's properly finished with lacquer will look good for a lifetime. When your cabinet came off the assembly line, it was finished in lacquer, not covered with wax. I have better things to do than haul out all of my things for rewaxing every now and then. If you enjoy waxing, save that for your car
Just my $0.02.
Phil Nelson