An advanced degree with more courses can only make your application stronger. I think what they look more for is what have you been doing or have done to make your application stronger as reapplicant. They want to see you prepare yourself and better yourself as a reapplicant. If you bring nothing to the table, and just reapply without doing any additional course work, retaking the DAT, more dental experience, etc, then they definitely will not give preference vs someone who is applying the first time.
I am in the same situation as you, except I am finishing up a Master's degree in June and applying this cycle. Before I started the program, I was contemplating if I should apply during 2010 while I was doing my Master's. I asked an assistant Dean at a dental school for her advice. She said that if I did apply during my Master's, I wouldn't really be bring anything new to my application. They could wait for my Fall grades at the end of December/ early January but that is already way too late in the cycle to be considered. The only thing I have to show then, is that I am doing a program, but not how well I am doing in it. Another admissions person said the same thing. When you apply, you want to have everything there and ready for them to see and make a decision about you. You also want to focus on your Master's and not have to worry about interviews and secondaries and applications. If you don't have money to waste on an application cycle, I suggest you finish your Master's and then apply. Have everything for them in early in June and watch those interviews pile up (hopefully). I know it sucks to have another gap year (if you already had one), and for me, I've thought about entering school so late or whatever, but it's worth it. It's just one more year, and we have like 35 years of our lives to practice or whatever, what is one more year. Just make the best of your year off.
Also look at the schools who's accepted more people with advanced degrees, or find out which schools look at your advanced degree GPA vs averaging into your cumulative GPA. I am going to finish 36 credit hours of classes and that is only boosting my GPA up by .11 points. Some schools look at them separately.
Good luck to you and everyone else who is or will be a reppalicant. I definitely know how sucky it is to not get in the first time but keep at it, we'll make it.