The Collaborative International Dictionary of English v.0.48:

Insipidity \In`si*pid"i*ty\, Insipidness \In*sip"id*ness\, n.
   [Cf. F. insipidit['e].]
   The quality or state of being insipid; vapidity. "Dryden's
   lines shine strongly through the insipidity of Tate's."
   --Pope.
   [1913 Webster]

WordNet (r) 3.0 (2006):

insipidness
    n 1: extreme dullness; lacking spirit or interest [syn:
         boringness, dreariness, insipidness, insipidity]
    2: lacking any distinctive or interesting taste property [syn:
       blandness, insipidity, insipidness]