How can I find out whether wind power is a practical option for our location on the Oregon coast?
If the actual average speeds at your exposed location are in the 10- to 12-mph range, you should be in good shape for a grid-tied wind system. To quote the site, "Annual average wind speeds of about 11 miles per hour (mph) are generally needed for grid-connected wind generating systems to be an economical resource. Annual average wind speeds of 7 to 9 mph may be adequate for electrical or mechanical applications for water pumping, residential or small on-site commercial loads."
Oregon State University has a wind-energy resource website. Their data for nearby coastal wind-site locations 111 and 112 show average annual wind speeds in the 10- to 12-mph range. The University may also have anemometers and other measuring devices available to borrow—you might want to do your own research on-site.
The Energy Information Administration of the U.S. Department of Energy also has pertinent national wind data. Their maps show virtually the entire Oregon coast as a minimum class 4 ("good"), with average wind speeds of 6 miles per hour.
There is also a NOAA (National Oceanic and Atmospheric Administration) website with Air Resources Laboratory data in the form of wind roses. These are diagrams that show average wind speed, direction, and duration for a particular place.
Finally, I notice on the Google Earth image of your town that there is an airfield just inland from the town. You might check with the airfield's air-traffic office about the typical wind speeds and directions.
As you noted, installation height often does matter. Local obstructions near ground level can make a huge difference in average wind speed, so if your house design, the neighbors, and local zoning laws allow you to put the windmill high up in the air, go for it.
By the way, it's not clear that your 80-percent overcast would preclude photovoltaics. Our area of San Francisco is typically foggy for much of the summer, but still gets 90 percent as much solar gain year-round as the sunny side of the city, with its more Mediterranean climate. Don't give up on photovoltaics, especially if wind power doesn't check out.