One thing that should be said ... it is likely that the difference in sound between the 100II and 120II is smaller than the 120II and the 240. It's not just a fancy case and native DSD playback, but the circuit design and amplifier as well. Additionally, if there is a chance you would use the 240 over its lifetime as a source component on a quality speaker system, that is another reason to consider its purchase.
Sometimes in determining which item to buy, we think mainly of our current needs. Given the lifetime of these devices, it's not a bad idea to anticipate our future needs as well. If resources are an issue, then certainly go with what seems to fit your current needs; however, if the resources are easily there to purchase a better unit, I always suggest doing so. Although the whole process of upgrading can be a fun experience, in the end it is more costly than to just get the best available within one's means.