Hey Jonathan,
I committed your latest search-plugin.tcl into scripts/guiplugins/search-plugin, overwriting my original, simple one. I put it there because I'm adding it to Pd-extended. I think it makes sense to just include your plugin directly rather than as a remixed helpbrowser.tcl. I also just committed a check that makes sure that pd-gui doesn't try to load a plugin that has already been loaded. That way when you make new version of the search plugin, people can just drop it into ~/pd-externals and it'll override the built-in search-plugin.tcl.
As for scripts/guiplugins/search-plugin, feel free to take that over and do whatever you want with it. I can't see a reason to keep the old one around any more, your search plugin is very thorough.
.hc