If you have some time, please visit OnlineCasinoSpecialist.com and check on the meta declarations I've set on each page. You would find that I never really observed siloing on each page, but mainly helping crawlers to better understand my pages through areas where I can extend keyword hints while never losing a chance to optimize (keyword rich and readable) the title and meta descriptions as I understand they are the main factors for conversions when the site already hit first page on a very competitive query.
First highlight: it would be to declare keywords that greatly help identify the page. ex. bingo page - I titled it 'Online Bingo Game Guide' since that is what the page is all about while on the meta keywords, I declared online bingo, bingo game, bingo guide, tips - keywords that help crawlers categorize the page on the index.
Second highlight: Yes. you can observe this with what I did with the bingo page we have. Meta keyword is another way of telling crawlers what the page is all about. Thus, one of the ways to relay page keyword hints to them. Please note that keywords declared on meta keyword are not necessarily the keywords you target for the page, but are words that contribute a lot to crawling agents' reading and understanding ability.
Third highlight: It is indeed important to define keywords. And it is also true that it is not only with meta tags that you can do it. You might want to spend time reading the search engine ranking factors compiled and rated by SEOmoz -
http://www.seomoz.org/article/search...anking-factors