Hey! I got in my first round without getting my undergrad in SLP. Though grades, experience, and GRE are crucial, I think putting a lot of effort in the statement of purpose is SO IMPORTANT. I can't stress it enough. If you think about how many applicants they get, most who are serious about SLP are going to be competitive applicants with high scores and years of experience. I volunteered for one summer at a speech therapy camp and I didn't have a high GPA nor high GRE scores and I got into a top program. I think all the effort and thought I put into my SOP really paid off.
The SOP gives you a chance to let the committee know who you are as a person: Are you a leader? Are you curious to learn more about the field of SLP? What kind of goals do you have for yourself? It also gives you the chance to tell them specifically what got you interested in pursuing SLP: how did your experiences lead you to now (please stay away from the cliche family member who has a stuttering problem)? What about dysphasia makes you excited? It also gives you the opportunity to let them know why you're interested in THEIR specific program: Which professors would you like to conduct research with and why? What is it about their program that sets them apart from the hundreds of others out there? How are you going to positively impact their program? I think these questions are important to consider when drafting out a SOP.
All in all, the SOP allows the committee to set aside the numbers and to really qualify your application. They're really looking for people who are goal oriented, go-getters, and who they think will succeed in their program as well as in the field. If you think you can, verbally tell them through your experiences, leadership, and dedication!! I hope this helps