Thank you for the trip report. I also got one of the intro $99 fares from WOW but, I don't fly until September. And like you I'm flying Icelandair back. I've been curious about the WOW experience from SFO. Especially in regards to seating. Looks like I may just pay for a regular assigned seat. I'm taking it as a personal challenge to only take 11 lbs though. Of course I'm bringing a coat with lots of pockets.
I'm curious if you just stayed at the airport until you caught the bus to the Blue Lagoon? The 4 am arrival has me stressing out more that it probably should.
I didn't know the Centurion had a sparkling water tap! I guess I never get water there. I am going to need to find that.