Many people like to purchase on the West side of 1st in Normandy Park because of the Schools (Marvista is the desired Elementary School). Also, it's a little difficult to get a view from the East side of 1st Ave. As someone already mentioned the further you can get away from Pacific Highway and Airplane noise the better.

I think west of 1st and N Park is a nicer area. Maybe you want to be farther from the airport, closer to Burien down town or in a quiet neighbor hood over the hill in the wooded areas up from highline. We looked in that area and just based on the neighborhoods narrowed it down to west of 1st just by the vibe we got in the neighborhoods not even considering the price.

It's just one of the market quirks. Every area of the US has pockets of real estate that is more expensive than the one across the street. 1st Ave in Burien is just like 6th Ave in Tacoma. I lived in Des Moines, WA for 30 years so I am very familiar with the area. Normandy Park has always been desireable. For as long as I can remember they have promoted themselves as a "boutique" neighborhood and have created exclusivity and demand for homes.