You are referring to preferred provider networks, and yes insurance companies can negotiate discounted rates. Most of my experience is with Kaiser which is a non-profit and typically the negotiated rates are 80% of medicare. I don't know how this will impacted for-profit medical providers.

My understand of the impact of this again, just goes back to medication reimbursement. Rates will go down. I don't know how this will impact offices visits etc under the complexity ranges. I would suspect only a small percentage of patients are actually doing uninsured walk ins and paying out of pocket rates.

I think the impact of this might only impact people shopping around for for certain non-critical care if they are paying out of pocket. I would think certain specializations will be more heavily impacted. Dermatology with cosmetic removals comes to mind. People might shop around for that. If you are planning on paying for a major inpatient surgery, you probably have insurance or couldn't afford it out of pocket. If you could afford it, you probably aren't concerned about the price.