My house, I would get it replaced. That high of pressure is not good on appliances like your washing machine and dishwasher.

Being at 80psi when they tested it does not mean it could be higher at different times of the day. IMO.

below is a link to water pressure from a municipal utility website stating why you need a pressure regulator

Here is a link that might be useful: water pressure

Does $398 sound like a fair price? I am in Kansas City.

If your water pressure is 80psi and your current valve will not repond to adjustment I would definitely recommend you change it out as soon as is practical, but don't panic, it is not an emergency situation, just one that should get immediate priority attention.

Normally I do not endorse any specific manufacturer or product but in this case I would like to make an exception. WATTS MANUFACTURING CO is without a doubt the worlds leading producer of Pressure regulating or pressure limiting devices such as Commercial High Pressure Boiler Safety Valves, Residential boiler safety valves, water heater Temperature & Pressure Relief Valves(T%P valve) and water service Pressure reducing Valves (PRV). In my humble opinion when selecting any safety valves or pressure limiting valves WATTS would be my absolute first choice.

For Residential Water service I would recommend the WATTS Pressure Reducing Valve series 25AUB-Z3 which is available in sizes ranging from 1/2" to 2" and the prices typically range about $75 to $125 depending upon size.

The Watts reducing valve body has a Female Iron Pipe fitting on both ends and one end has a union function so it is basically an easy changeout. In my opinion this project would be well suited to anyone who has moderate DIY skills in plumbing.