the 5 was a big fail in worldwide LTE Band support (doesnt affect people in the U.S.)
so upgrading from the 5 to a 5S or even 5C could mean for a lot of people that they will get LTE the first time on an iPhone.
Depending on where you live that alone could justify for an upgrade.
Everything else is fine on the 5 and if your upgrading to a 5S now for other reasons then need of LTE you will surely upgrade to the real deal (iPhone 6) next year again.