Sure it's been covered, but;
- will you use a bigger screen?
- will you notice the difference in speed?
- will you actually use 4G or are you in an area that currently has it (i.e. London)?
If the above answers are all yes, upgrade.
When the 5 came out and 4G wasn't available, none of the above bothered me, so just stuck with the 4S for another 12 month contract.