Yes if you get a pen and tablet with pressure sensitivity you'll be able to use more functions of many brushes as well as adding it to brushes that dont already use it for some cool effects.
I'd recommend the Wacom Bamboo Fun for a first tablet. Its the cheapest of their range but is very good for a starter.[link][link]
(I have the bamboo fun which has served me well for over a year now but I think they've made the basic bamboo better so not sure which is the best of the two)