Every player has his price. Van der Vaart cost 8 million I think, but he wouldn't have joined Villa, same as Suarez really. I think if they're being realistic, Bent is someone that would join them, but yeah he is overpriced at 18m, let alone the 24m that's been mooted (never used that word before, felt good). So no, Bent is not not worth more really in terms of how good a player he is, just don't think there's many other better options out there for Villa.
I think someone told me he was the 3rd highest premiership scorer over the past 3 seasons? My near 20 goals a season stat was totally made up, but I bet it's not a million miles wide of the mark =)