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It will save the file the first time you press ⌘P, a second press opens the Goto Panel.
Modifying word_separators also breaks "Select More". While it works from the menu (clicking Selection→Select More), the shortcut (⌘D on Mac OS X) fails.

Steps to reproduce this problem:

1. remove '?' from word_separators

2. move cursor inside word "?MODULE"

3. press ⌘D, ST2 selects the whole word "?MODULE"

4. press ⌘D again, status bar shows "unable to find \b\?MODULE\b"

How about listing all build systems that are applicable to the current file
in the quick panel, then run them when they are selected.
Another possibility would be creating commands for all available build systems (dynamically) so they're available through the command palette. 
Wouldn't this mean that all menu items need to be available as python API commands?
This is probably a good thing, too...