Google Webmaster Tools shows when G reads the sitemap indexes; it may take a day or two to digest once it does read it. Until then the changes only matter once the viewer gets to the site.
That's not always the problem. I too have made recommended changes, and have gotten clobbered. In my case, one such problem came with reducing the number of times the keyphrase is found in the document text. SEOmoz's page analysis is based strictly on count, not percentage. So mentioning it at least 4 times but no more than 14 is not a help on longer texts, or for that matter on some short ones. There's only so much I can do to use certain core words less often; beyond that, it becomes poor English, which would drive away users who come to the site. I would think Google accounts for that with some sort of text (not file) length keyword/phrase percentage in their algorithm, otherwise it would weigh solidly against authoritative pieces. But on keywords in document, what's good for Google seems not to be good for Bing, and vice-versa. And recent changes in Google's algo (as reported on the SEOmoz monthly top 10 recently) may well make it even more sensitive to supposed spamming on keyphrase in document.
That's just one of several such problems. The engines have their own internal contradictions, too (Google re Google services and page speed, for one). You can't get rid of them all.