Rich -
Have only limited experience with the OP streams but I have found that most of the major Western Washington river systems have decent to excellent resident trout fishing. The headwater fisheries you referred to are the most consistent. My general plan of attack is go to my topog. maps. I look at the upper reaches of the larger tribs or headwaters of the mainstem. My best trout fishing is almost always in those streams where I can find a fairly long section of flat gradient (1 to 4%) above anadromous barriers or steep canyon sections. Most commonly I find rainbows or cutthroat. Getting even a 1/2 mile of the beaten path can lead to some very nice trout fishing (high catch rates in solitude). The fish aren't large; typical 8 to 12 inches with a 14 incher being a lunker. The nice thing is that they tend to be naive and not fussy about patterns or fancy ties - I like to use dry flies, mostly caddis, bucktail coachman and other high floaters; sizes 10 to 14s.

If you are looking for larger fish then I would concentrate on the upper portions of the larger maintstems looking for out of way canyon and bed-rock pools. Almost all of the streams have few large rainbows (14+ inches). The last hour of daylight can sometimes produce surprising dry fly fishing otherwise it is mostly nymphs except when some exceptional bugs (example stones) are hatching. Catches of a couple fish would be the norm. Streams with bait bans, restrictive regulations, etc generally tend to have older fish. Be prepared to be surprised by the odd summer steelhead or bull trout.

Finding these fishing gems is very rewarding but the best may be the search - good luck and enjoy!!

Tight lines
Smalma