First a few things. I dont think you can look at warranties as not worth or worth it as a general sentiment. It all depends on the failure rate of the product. In the case of the iphone 4/4s it had a very very high incident of glass breaks but overall a very very low failure rate on everything else. In that case, a $99/warranty may be worth it since that plus the $49 is still cheaper than an on warranty replacement. Obviously the failure rate (including glass breaks) will go up significantly if you dont use a case).
On the iPhone 5, a few changes. First, the phone is shown to be much much more durable in 3rd party tests. In fact, it may be one of the most durable phones out there. Time will tell with this but its promising. Additionally, with the new design, and the glass and touch sensors being integrated, it is now very easy for them to swap out the front glass. All Apple stores or most will be equipped with devices capable of quickly changing the glass. On previous models, the front glass breaks = new phone.
What does this mean for OP? If you use your phone naked and it gets banged up and you want to "Accidentally" break it to get a new clean one, chances are that if you do this by breaking the glass, you are not going to get a new ones. Just glass replaced. If your only concern is breaking the glass, id say get the warranty for the peace of mind and go naked. But if you are highly anal about your device and treat it like a watch, then your choice may not be as easy. You are very likely to scratch it up at some point over two years. Sure you could always slip up and drop it in the toilet but that is for you to decide.