Yes you will lose the apps you currently have and it won't work with maemo apps. But otoh you will open up the possibility of installing lots of new apps. As the differences between GTK+ and Maemo are small, you could refactor your map app to just be a GTK+ app (assuming you don't use any of the Maemo-specific libs).

This is the feed browser for the Ansgtrom project (Poky and Angstrom use the same base metadata to build their files): http://www.angstrom-distribution.org/repo/

Try it and see, it's just a case of a rootfs and kernel individually.