I know that it certainly helps. Any "graduate" experience, be it lab work or upper level courses, looks good to adcoms in masters programs. I really didn't have that many upper level courses done when I entered but I had myriad lab experiences which reflected what I would need to do to finish a project with my mentor. I showed that I was already familiar with the work that my mentor performed and that coming up with and finishing a project would be a very viable thing for me to accomplish. Yes, they do look at your grades, and if you do well enough on the DAT then they may (depending on the program and university) take that score in place of the GRE which I was very greatful that I didn't have to take. More than anything though, they will probably admit you if you look ambitious, pragmatic, and resourceful to your mentor that you will facilitate to pump out publications with. They really want someone that can "contribute" (key word) to the department. I also know that it must help that you've actually had adequate lab experience and good relationships with faculty of the department you want to do a masters in. That said, I had a friend who had okay grades and a 20 DAT score but he didn't know anybody really. He did interview but was ultimately rejected and I really don't know why. I am just greatful that they accepted me. I know that for my class we had about 75 applicants to the Physiology program for 5 spots. Generally, they have about 60-70 applicants for 4-8 spots so you have to be competative. Just show them that your passionate, be excited, meet faculty, be familiar with their research, become their friends, maybe do some lab-work, have a reasonably successful academic background and I'm sure you'll get in. Keep in mind that this is how I saw it at BYU. It may be different at other universities. Good luck!