If you really want to be like Newton, you will not be hurt by practicing computation. I also think most people will appreciate the extra explanation and examples in Munkres. I know when I taught out of Spivak to average math majors at a state school, Spivak was impenetrable to them. Munkres is writing here from years of experience trying to explain this stuff to his many students at MIT. Munkres devotes 380 pages to the topic in comparison to Spivak's 140. This will not be considered a flaw by everyone.
"Obvious" things are not always as obvious as one hopes. E.g. Mike himself corrected one inadequate argument involving partitions of unity in the theory of integration from his first to his second edition, and other subtle flaws that had escaped me have been pointed out by some analyst friends. I agree with you that I myself would probably prefer the Spivak book, but many students might benefit from the fuller version of Munkres.
Indeed after reading the preface to Munkres, I conjecture that he began by teaching from Spivak and gradually wrote his own book to fill in all the missing background he discovered in his classes over the years. This means the book can be expected to all be necessary only to the weakest member of the class, and the others are well advised to select from it what they need. Such a book can serve more people than one that is accessible only to the strongest.
I agree that Spivak is a beautiful book, intended for those who want the briefest possible treatment of the essentials of advanced calculus. (It omits however the theory of existence of solutions of differential equations, unfortunately, as does Munkres also I believe.)