Maybe you posted when most of us who have been to Reykjavik weren't online?
I've been there many times, never stayed at a Bonvoy hotel. Last time I stayed in Reykjavik, though, was before the Starwood merger and I don't think there were any options there.
Anything in the 101 post code in Reykjavik is well located for touring. I am pretty sure there is at least one property that qualifies.