The 5s is a far from a joke. This type of finger print recognition on a phone didn't exist in 2011. Or 2012. It's new and its extremely nice, fast and a welcome way to secure your phone rather the pass code alternative
Nor do you understand 64 bit computing.
To the OP...you don't mention the phone you '...lost'? Are you tied Into the iOS system? Apps, movies, books and magazines, et al? If not, give it a shot. You'll know within the return period (if you've been an iOS user) whether or not you'll want to hang on to the s4 for two more years.
IMO, The iPhone 5s is an excellent update to the 5. It's also a different idea and philosophy in comparison to the s4---as is iOS period. I own both an iPhone 5 and Galaxy Note. I like them both quite a bit....but if it ultimately came down to one or the other, my iPhone isn't going anywhere. We've got the 4s (wife) and I the 5. We'll be buying a 5s next week...and selling the 4s to subsidize the subsidized cost
J