There are certain history entries that are less important, depending on the use-case they cover. Downloads fall into this category, since it's less likely one needs to get a download from months ago, and we still keep the originating page (from which the download started) in history, for any purpose. I'll also file other bugs for redirects and other less prominent visit types, so if possible this code should take into account future additions. Keeping more useful data also means returning better results in the awesomebar.
This may still be something good to do, though Alice pointed out a possible use-case for history, that is visited link coloring, to know which files have been downloaded from an ftp or such. History is valuable so this needs more brainstorming before being considered a solution.
hidden pages are not that interesting to keep though, so would make sense at least for those to make space to more meaningful history.