We paid out of pocket for our SPD eval with Dr. Balzer-Martin and recommend it. Although SPD isn't turning out to be what triggers our child's behaviors, we started private weekly OT based on her recommendation, as it couldn't hurt. What I like about Dr. Balzer-Martin is that she ONLY does evals, so it isn't in her interest to find something as she doesn't provide the OT. She also will provide you with an itemized reciept with diagnostic codes that you can submit to your insurance for partial reimbursement.
We have BCBS federal standard, and I called my insurance and basically dared them to find someone in a 10 mile radius that is an OT specializing in preschoolers with SPD, Connections Therapy Center:
http://thectcenter.com/. I was totally expecting to have to pay out of pocket. Turns out, they found someone in Lanham and we're really enjoying working with them, and it is only a $20 co-pay per session. Not sure who you talked to at your plan, but I pushed through the prompts until I found someone to help me with identifying providers. If Aetna isn't working for you and you can switch plans, do so. It might take you that long to get an appointment and go through the eval process anyway.