I'd say waiting is a good idea to be honest. But that's because I've never jailbroken a product. If you do want to jailbreak it, then I'd probably follow the above advice saying get 1 now. For the afore said reasons. You can't be certain Apple won't stop the jail breaking of their next iPod touch.
However, it is of course possible that Apple will keep selling the iPod touch 4G 8GB version and only offer an iPod touch 5G with 32GB and 64GB memory.