Nope, since I'm also on the S cycle. Even with the 6/6 Plus coming out, I've only had my 5s for 14 months and don't really see the need to upgrade (especially since I like the 4" form factor).
Design change and lots of new features, or microarchitecture and performance upgrade -- take your pick.
The A7 was a radical step up in the processor design, and it moved the platform to 64-bit. The A7 used a completely new processor design that departed from both the prior design and the ARM reference design. All of this doubled the processor performance between the 5s and 5.
The A8 was a radical power consumption reduction that accommodated a major design change (i.e., larger screen and doubling the processed graphics resolution). Processor performance increased by only about 20%, but the power consumption was reduced by half. The A8 did not see major changes to the microarchitecture, primarily optimizations and a die shrink that cut the power requirements.
If Apple follows the same "tick-tock" alternation between the microarchitectural design and the die shrink/process changes, then the A9 will likely keep the power consumption constant (since the 6s would presumably share most of the internal design with the 6) while redesigning the CPU for a big bump in performance.
The triple-core A8X processor used in the iPad Air 2 already hints that Apple might also have a major change coming with the GPU, by going with their own custom design. The three-core design also hints that Apple might be ready to branch out beyond the dual-core CPUs they've used since the A5.