Truthfully I don't think the S5 is worth the money if you have an S4. The increase in performance is too small to justify the price. Additionally, since the GS4 camera is already fantastic, this too, is not worth the upgrade. The fingerprint scanner is cool and all but you should consider how much that really means to you realistically if that's all you have left to persuade you.
Now, I have a Galaxy Note 3 and while I am almost certain the Note 4 will be a small upgrade as well, I will probably get it but only because I have that T-MO JUMP thing going for me, so why not? If you or I are paying full price, certainly not worth it (but if you can sell your current phone for a good price, go for it).
Check out some benchmarks and...