OK, a couple of hours later here it is. Not pretty but functional, a page that will generate a 20 track playlist within a given tempo range from artists similar and including the chosen artist.
Give it a whirl Daniel’s Artist Tempo Spotify Playlists generator. It wont play directly in iPhone but you can easily take the playlists to Spotify. Thanks to www.musicmachinery.com for the inspiration and a good chunk of the code… I didnt have time to learn jQuery in an evening.
UPDATE. Two days later, I’ve now got a home-brew app running inside Spotify itself that will generate playlists using the various EchoNest filters. It was a bit fiddly involving getting a developer license from Spotify. I can’t share it with you except as a picture or as source code… mail me if you are interested, it’s along the lines of the linked web page above but more user friendly.