[1] I have been blessed beyond measure in having friends far wiser and
more learned than [I __ ].
[2] I have been blessed beyond measure in having friends far wiser and
more learned than [me __ ].
[3] I have been blessed beyond measure in having friends far wiser and
more learned than [I am __ ].
All three comparatives are possible.
If the pronoun is understood as subject , as it is here, the choice of case depends on style. In formal style it appears as nominative, [1], just as it does in the unreduced clause, [3].
In informal style it is accusative, as in [2] where the missing verb cannot be inserted.
I suspect that most speakers would find [1] excessively formal and [2] obtrusively informal, and opt for [3]. I know I would.