Driftwood plays an important role in local shoreline ecology, helping to trap moisture and provide shade for the developing eggs of small fishes that spawn high on the beaches during high tides. Those small fishes are in turn food for all kinds of birds, larger fish like salmon, and small marine mammals like harbor seals and porpoises. I don’t know that there are laws preventing private landowners from removing driftwood from their beaches, but I wouldn’t encourage it.
I don’t think the driftwood you’d find on freshwater river bars serves the same ecological function, so that might be an option, as long as there’s no legal reason not to remove it.
If you’re interested in coastal landscaping, restoring native coastal prairie might work for you too. See this for more info: http://community.seattletimes.nwsource.com/archive/?date=20071127&slug=webcoastprairies27
Washington Native Plant Society (http://www.wnps.org/index.html) can help you find the right plants…if you’re interested, let me know, I have lots of camas bulbs that could help get you started.