Definitely not a problem to have both! Even though they share 6 of the machines, they sound completely different on each device due to the available headroom. The workflow is immensely different as well. The Cycles has machine lock per step and you can use Control All on the Machine for insane improv fun. The Syntakt has Trig Preview, which in my opinion is essential for per step sound design, and of course the analog machines - which sound REALLY good.
I create entirely different material on each and I think that makes worth it to have both. I use the Cycles for single pattern improv stuff while I create full tracks on the Syntakt.
Of course, I also have the DT and DN so going down this road could get expensive =P