The Collaborative International Dictionary of English v.0.48:

meaningfulness \meaningfulness\ n.
   the quality of having great meaning or value.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

meaningfulness
    n 1: the quality of having great value or significance [ant:
         meaninglessness]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "meaningfulness":
   articulateness, command of language, command of words,
   effective style, eloquence, eloquent tongue, expression,
   expressiveness, facundity, felicitousness, felicity,
   gift of expression, gift of gab, glibness, graphicness,
   intelligibility, interpretability, meatiness, oratory, pithiness,
   pregnancy, readability, rhetoric, sententiousness, significance,
   significancy, significantness, silver tongue, slickness,
   smoothness, suggestiveness, vividness