Re: XKCD has been totuting the complexity angle for years
"This is my core passphrase (which never varies); it's easy to remember. The unique extension for this site or service is: The Register."
Thing is, dictionary attacks are wise to tricks like yours, and the first things they'll try will be capital shifts and "1337 speak". Plus, anyone who finds one of them can take stabs at your formula, or just hit you a second time to get enough of a delta to figure it out.
As for the password manager things, that doesn't work if there's nothing under the person's safe control. Then you double-whammy this with a really bad (as in "donkeyenginepaperclipwrong") memory.