Why not pull them out? And try to sell your unused pins to someone who has not enough I/O pins ;-)

I don't think it matters wheter you pull unused inputs high or low. To be on the safe site you should use a pull-up or pull-down ressitor to avoid high currents is one of the pins is driven to an opposite level by mistake.
Tying the pins to a "legal" level will protect your chip better from unexplainable lockup (or destruction) caused by ESD. And CMOS inputs that float draw more current than when they are tied to one of the supply rails.

Happy programming, soldering and designing