Definitely agree with this. I had a relatively low GPA for clinical (80% avg) and an okay, but not great GRE combined score. Applied to 3 programs (only 1 clinical program), got into 2--including the best one I applied to.
Research experience means a better CV, potential presentations/publications, and more experience with faculty = more thorough letters of recommendation. Furthermore, if you have a lot of experience in one subject area, it can really help you craft a statement of intent directed for a particular prospective advisor.
IMO: much easier to distinguish yourself with solid research experience, than it is w/ GRE/GPA. Be confident in what you know. Be confident in your skills. Be confident in what you want to research in the future; you'll likely have a better idea of what you want to do than other students with less research experience. Be confident in how the particular faculty compliments your proposed program of research.
My program accepted 8 students (unusually high), and I had the worst GPA/GRE of all of them. I was terribly underdressed for interviews. I also said during interviews I wasn't really interested in clinical practice--I was (and still am) interested in research with this particular supervisor. Once you're in, people don't care about grades. They care about your research productivity, for which you'll be better prepared.
So, gauging from what I've been reading, it may be uncommon for average GRE scores (and GPAs) to get into really good PhD Clinical programs, but in my case, it was possible, and only because of my research experience.