Well, what's your time on Fridrich method? I say that it is NOT worth learning ZB until your times are consistently below 14 seconds. Someone who did when they were around 13 seconds only improved to 12 seconds. This is because case recognition on ZB is extremely hard to do quickly.
For the Fridrich method, do you know:
-Full OLL/PLL. Even if you do, you might as well make sure you can perform every PLL in under 3 or 4 seconds.
-F2l tricks, such as working corner/edge, maybe even some algorithms. http://jmbaum.110mb.com/f2l.htm
-How to do cross on bottom in less than 8 moves on average?
If you want to learn something new, how about becoming colour neutral? Or you can learn one handed cubing (usually for 3x3x3 only), blindfold 3x3x3/4x4x4/multiblind/etc, or even a blockbuilding method such as Roux. :3