I suspect it was more a case of leaving the door open. You're right, the ending, whilst tying up a lot of the story threads, was in effect a new beginning, but judging by the length of time it took him to write the eventual sequel (18 years) and the fact that when it did appear, it was co-written (with Thomas T. Thomas, an occasional collaborator of Roger Zelazny's) I doubt if he had any specific intentions of a follow-up at the time.The end was of Man Plus didnt feel like an ending. I wonder if he planned on a second book when he wrote Man Plus.
I think i saw Wolfbane in SF masterwork series list.
The Space Merchants i know from somwhere too.
The Space Merchants is in the SF Masterwork series (No. 54) -- and I can't recommend it highly enough. Wolfbane isn't (although it would make a great addition if anyone from Gollancz ever happens to read this ). However, it was part of the Gollancz Collectors Series that came out a few years back --the oversized paperbacks with the striking yellow covers and the cigar bands -- which is the edition of the book I've kept.
Good luck with finding one or both!
I've read only Gateway, but I didn't like it because the end didn't explain anything. I suppose some people might like the book because it is mysterious to the end.
But I thought the book was a bit boring, and I had to make myself read it to the end in the hope that there will be at least an answer to the questions, like who the aliens were etc., but there were no answers, so I was disappointed.