The Collaborative International Dictionary of English v.0.48:

Misspend \Mis*spend"\, v. t. [imp. & p. p. Misspent; p. pr. &
   vb. n. Misspending.]
   To spend amiss or for wrong purposes; to squander; to waste;
   as, to misspend time or money. --J. Philips.
   [1913 Webster]

WordNet (r) 3.0 (2006):

misspend
    v 1: spend time badly or unwisely; "He misspent his youth"
    2: spend (money or other resources) unwisely