I'm sort of half-tempted to read the full, expanded version (from 1991), which is 60,000 words longer. However, I suspect the editors did Heinlein a huge favor.
That's usually the case, but in this case, I think the expanded version is much better. I read it when it came out in '91, and thought the additions made the novel flow a lot better, and cleared up some dangling questions.
I read the "expanded" (unedited) versions of "The Puppet Masters" and "Red Planet" and in both cases found some of the "extra" material intriguing, but overall preferred the shorter, edited versions. I've also heard that the shorter, originally published version of SIASL is now out of print and the only version you can now buy is the expanded one. If this is true, it strikes me as a little odd, to say the least.
Nice cover. Never seen that particular edition.