Rick --and guest,
Size does matter. So does joint flexibility.
Not to minimize the importance of improvising, practice, etc., but ceteris paribus longer fingers and the ability to bend a finger backward at one or more joints is a real advantage--and there are some chord positions that are physically impossible for some people's hands.

I know, I know, Segovia had short stubby fingers, and he did o.k. But sometimes folks with reallyshort fingers [even for a woman] and finger joints that bend only one way have to find alternatives to the methods others can use for playing some chords. [I, for one, simply cannot hold down two strings with one finger--except, of course, for the barre finger--unless they are at the edge of the neck.] As "guest" suggests, "these damned wrinkly fingers" sometimes make the theoretically ideal positions rather unattainable.
I love the C9 chord, but I cheat it, holding down only the 2nd, 3rd, 4th, and 5th strings, because my fingers are not double jointed. Thus, it sounds fine as a C9 but is not moveable to all positions on the neck.

Mooh and Rick
I really like sliding b7 up to the next fret for a modified C7 and back.

Justa,
I'm gonna have to try that Merle Travis E6th/13th thing as soon as I unpack my guitar tonight.

Genie