then why read Hanson also? if they are colleagues and co-bloggers there must be something about EY that Robin thinks is first rate, no?

Not necessarily. Hanson might be a good thinker who is also a personal opportunist who'll do anything to enhance his status, where co-publishing with Yudkowsky helped put Hanson's blog on the map. Hanson could have "admired" Yudkowsky for his fan-club building capacities rather than for the high quality of his thinking.