Excellent points, M.Ted. Let me add, in regard to my two of my favorite keys and Old Folky's as well:

C allows you to "walk" the bass from C to Am and/or to F and to G/G7 using open/2d fret/3d fret on the three low strings, using middle and ring finger, AND to pick melodies on the top two or three strings, open and at the 1st and 3d frets, using forefinger and pinky.

G offers most but not all of the above features of C.

I've been thinking along these lines as this thread has developed. Different players seem to favor different keys (actaully, different key "shapes" or "fingerings" which can be adjusted to the actual sound of additional keys by use of the capo).

I lean heavily towards C (and to a lesser extent G) for most non-blues songs, and towards E (and A) for blues, and I'm a fingerpicker and a "bass-walker."

I am very much aware that plenty of folk-type players have a similar affinity for the key of D, and I think that, for whatever reason, this penchant seems to go hand-in-hand with an interest in, and ability to utilize, alternative/open tunings ~ especially open-tuning work that is not blues slide playing. I wonder why that is?

Maybe they get started by dropping that bass string from E to D and then can't stop themselves... My other theory, even more vague, is that players who favor D might be more harmonically ("chordally") oriented than us bass-note/melody-note C pickers... ????