I feel sure such songbooks were put together by people who had no regard for guitarists.

Well, they may well have been put together by people who had some regard for singers... :-)

If it's a song you're dealing with, then key is paramount, and the most important thing is getting the key that suits your voice, regardless of the written key.

Once you've established the key, then how you voice it is up to you. By 'voicing' I mean the choice of chords, regardless of key. So, if the key that suits your voice for a song is F (say), and you like playing chords in C, then capo-ing it on the 5th fret, singing in F and playing (voicing) in C will be your combination.

But... sometimes it's more fun and gives a more original sound to play it in the real voicing. If your song's in F, then you might play it in F - you'll certainly sound a little different that way.

All depends on what style of material you like to play, of course.