Many of them, at least, are grayed out for good reasons.
Some, like "Google Scroll", are grayed out because they have been deprecated.
Others are grayed out just while you are seeing a page they don't work in; when you reach a page where they can work, they will recover the color again. For example "RSS subscription by Google" would only work in those webs that offer the RSS service, and "Reddit enhancement suit" will be colored only when you are browsing reddit.org web.
Finally others are because you have hidden them (actually just its icon), you can restore them by rightclicking the icon and clicking "show in the toolbar".