It is a long time since I dived the Similians so I can't really comment on the coral damage but we used Sea Dragon for a live aboard who were pretty good, reasonable boats and good dive staff. The diving around Koh phi phi was really not very good and nowhere near the standard of the Similians.

I seem to recall that Hanuman posted something about the park being partially closed to diving a while ago so he may be able to provide some further info.

I haven't dived there myself in a couple of years, and the last time wasn't great (although still good). Reports from all my friends say it just isn't as good as it was before, and there are some sites that are still closed.

My friends who still dive the area regularly think Hin Daeng and Hin Muang are still very good. I did these on a liveaboard out of Lanta (3 days 2 nights), which is probably the way to go. They can be done as day trips, but then you tend to get there the same time as everyone else. I did the trip on the Flying Seahorse, which isn't really that great, but was good enough for a short trip. I'm not sure who else does the trip, but the Amazing Lanta web site would have the most current information.

I'm off to Pulau Weh tomorrow, which I'm hearing good things about. Will report back!

You are correct the damage is signifigant based on my cousins trip this year.