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The action I would recommend would depend on two factors: are there backlinks to the page, and how frequently are the links used (check Google Analytics). If you have a page without any backlinks that is rarely used, then I would allow the 404 to occur. If you have a page with link juice and is frequently used, I would make an effort to ensure user's are happy with what they find when clicking to the page, otherwise they may bounce off my site. In this case I would rebuild the content. 404s are a natural part of the internet. Content is moved and removed over time. It is not necessarily a bad thing for a 404 to occur if your site is prepared to handle it (i.e. your 404 page is helpful and friendly).The only point I am making is some webmasters view 404s as an issue with their site that must be resolved, and that is not the case. You should be fully aware of any 404 links and be able to adjust where necessary.

A lot of coders like giving filenames underscores rather than dashes, because when you select (doubleclick) a filename_like_this all the text is selected, whereas a filename-like-this may only have part of it highlighted - so to me, an underscore is more akin to 'treat this like a word' and a dash is 'treat this like a space' - and either is better than %20! For SEO though, the dash=space is worth it where: the URL string is long (thisisnotaseasytoread in the address bar, this-is-much-easier-to-comprehend) - I think that helps users, which in turn signals to Google that you're being helpful if the concatenation of the words would be confusing to a stemming programme - see here for examples http://independentsources.com/2006/07/12/worst-company-urls/ if someone wanted/had to manually type a url, a dash is quicker/easier as you don't need the shift key (which you do for an underscore) if someone shares (pastes) a raw, long URL, with dashes in you have a chance it will wrap in a blog or wherever - reallylonglinkswithnospacesendupstickingoutofthesidesofablogandlookuglyandannoyingandlessprofessional that looks dreadful, whereas you might get away with high-on-the-hill-stood-a-lonely-goatherd I find that it also helps with link-naming consistency, it's easier for you to spot your own typos or linking errors (so fewer 404s to hunt down) Sorry, must dash

also, keep in mind that if you are ranking on secondary terms on the non-front pages, you will lose a lot of that relevance by forwarding to only your home page (esp. if it's not about that specific thing. example: old site about fruit  on home page - old subpage about apples the old subpage about apples may rank really well next, you  forward the old subpage about apples to your new front page the search engines go "oh, this page isn't as relevant as the old apples subpage that no longer exists, let's bump down the rankings" hence, it's always best to forward your equivalent old content to your equivalent new content.

If your page content supports using UGC (reviews, comments, etc), this is an excellent way to get different spellings and vernacular of users into content organically. If it is written by users, then it's a very natural part of your content. As a member of the Bazaarvoice Advisory board, I see evidence of the great organic lift from reviews/customer posts over and over related to words and spellings that only UGC generates. Through this content, you optimize easily and have a chance to rank on numerous variations.