Publishing a paper is definitely good for a PhD. So are other things like academic awards, scholarships, being invited to conferences, etc. Anything that makes you stand out academically.
Now, if you are interesting in PhD programs in business, actually many do not require that you have the GMAT, so since you have been testing about the range at what you have actually got, I would say leave that alone. Your time would be better spent on publishing papers, getting involved academically, gaining teaching experience, going to conferences, etc.... all the things that PhD programs really look for.
If you like the post, give it a KUDOS!