Let me put it this way: if you fly round in circles overhead the airfield, what exactly are you going to learn?
The whole point of hour building is to gain experience and the only way to really achieve this is to push yourself outside of your comfort zone. Hour building is not just about putting numbers in a book, it is about developing yourslef as a pilot. Gaining your PPL is just a ticket giving you the ability to go off and learn. If you're getting 100hrs as a block why not go off somewhere for a couple of weeks?
I'm assuming that you are going on to do your CPL from the nature of your post, so ask yourself this: if you were a flight crew employer looking at a number of low-hours candidates which one would you select, person A) has 250hrs of dual and local area flying or person B) has 250hrs but has flown solo across the USA, been to place a, place b, really done some interesting flying, probably learnt a lot in the process.
Moreover, as a pilot, why would you want to spend 100hrs "killing time?" I have never flown in the US but there must be some beautiful places to fly and see, so go do it!