I haven't read the whole discussion, but I personally think that guitar playing must not become an obsession, especially for amateurs like most of us here.
Although you won't get anywhere unless you challenge yourself a bit more by attempting more difficult pieces the longer you play, it has to stay fun. Most people make the mistake to start on pieces which are way beyond their current level and that only leads to frustration. There is so much great guitar music out there which you never get to listen to, because everybody plays the same old pieces over and over again, just to prove that they can do it. Do you really want to hear another rendition of the "Romanza" (an awful piece in my opinion) or Recuerdos de la Alhambra? I certainly don't, because it gets boring after a while.
Pick music that suits your current level, or which is slightly more difficult and enjoy yourself. If you would like to play something which is not available as sheet music, try creating your own arrangement, something I personally enjoy very much and which will widen your knowledge about music in general and the instrument in particular. If you don't feel like playing on the odd day, leave the guitar in its case, because practicing without motivation will stay purely mechanical and won't get you anywhere.
Music is there for our enjoyment after all
Dringt durch des Aberglaubens Nacht, die Euch zu finstern Köpfen macht. Christian Fürchtegott Gellert (1715 - 1769)