How to substitute values on a page, without PHP?
This is even more new than Beta, but look at the Sandwich module that looks like most of its configuration is in 1 place (across all nodes of X type for instance).

The module sits at ~400 lines of code and has it looks like 2 small example usage modules/themes.

EDIT: to be clear this goes off custom markup I believe like, MY_CUSTOM_VALUE, in a body field of a node which would regex out to be whatever value you implement in a module. With page caching turned on shouldnt be a huge hit. You keep your "values" in code and dont depend on the Token module.