remdk: Thanks for your thoughts.
Arriving F, departing J, so I'll have access to at least one of the lounges.
I have the option to do a 2 hour layover, rather than 26, but I've never been to that part of the world before, so thought it was worth stopping over for a day to explore. Also, I'll be on the way from New York to Tanzania, and the trip will be in February. I really, really don't want to miss my connection and in February there is more than a small possibility of weather-related delays coming out of JFK, so wanted to build in a cushion. Sounds like it really isn't worth trying to do the tour -- I'll just get a nice hotel room in Doha, explore on my own on Friday afternoon/evening and head back to the airport Saturday morning.