Talking about old waxes, try giving this a read and see how old the compounds were in this. As long as the compound, looks, feels and smells (this is not for only one member :P) right you can use it.
As far as having old polishes/waxes goes which have become from a soft paste to a slightly more harder one, there is no harm in using them, obviously they will dry out faster since the solvent that keeps them in a soft paste has evaporated over time.
As per to the shine, ive noticed that aswell and usually attribute it to the fact that the wax gets more concentrated everytime the solvent dissolves from it therefore the better result though my experience has been limited to carnauba waxes only, most synthetic waxes run out before expectation
lol ..
Hope this helps. 
old school rub out?