> Kill it with fire ;)

One does not simply kill it with fire, will sent it directly to Mordor ;) Consider it dead.

> Please hold off with big changes to guides and evaluate the UI after GSoC has finished.

Looking forward to that !

> Why not greying out the menu option "View->Guides" when there are no guides.

This seems like an easy solution.

> Checkmarks
How about adding checkmarks/ticks next to the View menu items that are "on" (including all those in the Show/Hide submenu). Then users can clearly see what is "on" without having to toggle to check.

Related item, added a patch to toggle the guides on/off by clicking (without dragging) the ruler, useful ?
https://bugs.launchpad.net/inkscape/+bug/951580