I was lucky enough to fish on the KP last august/sept, and had a blast. We had lots and lots of pinks, quite a few silvers, and even got a very nice steelhead. Oh and about the Pinks, many folks will really kind of turn their noses up at them, but actually fresh from the salt they are quite aggressive and really fun to fish for; they do deteriorate pretty fast though once they hit fresh water. I believe it's the Reds that are often "flossed", from what I hear anyways. Sometimes good room to swing was not in the cards, but still found plenty of places to catch some fish.
We did float the middle Kenai one day, but honestly that was by far the low point of the trip as a whole. Lots and lots of boats, and the fishing was not as hot as we had hoped for. Also spent about an hour fishing at one of the drive up access points on the Kenai, and found about as great of a circus scene as I ever hope to experience. About an hour was more than we could take, even though the fishing was what I would consider to be "on fire" at that time. I'm not trying to be down on the Kenai river itself, but I would say that to really get into some quality fishing there you would want some time and/or guidance (and a boat). Otherwise there are quite a few other options further down the peninsula towards Homer. If you can I would try to work in a bit more time in that area, in part just for the scenery there... utterly stunning.
Have a great time on your trip, I can't wait to get back up there again myself!