The Collaborative International Dictionary of English v.0.48:

Impressionability \Im*pres`sion*a*bil"i*ty\, n.
   The quality of being impressionable.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

79 Moby Thesaurus words for "impressionability":
   accessibility, adaptability, affectibility, affectivity,
   agreeability, amenability, amenableness, aptitude, aptness,
   bendability, brightness, cleverness, delicacy, docility,
   ductibility, ductility, educability, elasticity, extendibility,
   extensibility, facility, fictility, flexibility, flexility,
   flexuousness, formativeness, give, impressibility,
   influenceability, intelligence, limberness, limen, litheness,
   malleability, moldability, motivation, movability, open-mindedness,
   openness, openness to sensation, perceptibility, persuadability,
   perviousness, physical sensibility, plasticity, pliability,
   pliancy, quickness, readiness, readiness of feeling, receptiveness,
   receptivity, responsiveness, sensation level, sensibility,
   sensibleness, sensitiveness, sensitivity, sentience, sentiency,
   sequacity, springiness, submissiveness, suggestibility, suppleness,
   susceptibility, susceptivity, swayableness, teachability,
   teachableness, tensileness, tensility, threshold of sensation,
   tractability, tractility, trainableness, weakness, willingness,
   willowiness