...why does a V-tail have better spin recovery tendancies?
It is known fact that increased dihedral or effective dihedral
(manifested in either the wings or tail, or both) helps to eliminate the spiral divergence mode, and helps recovery from
it. Because V-tails are essentially tails of very high dihedral, the aforementioned spin-helping characteristics are present...
(Am I confusing the spin you're discussing with spiral divergence mode? I know what the latter is, of course, but I'm not 100% sure that you're talking about the same thing as I am when you use the word 'spin'...)