If you have the money, get it. If you don't, wait. If you mean is is an upgrade from the z3c... Yeeah it's better in pretty much every way accept ram and screen resolution.
I debated the same thing and am very happy I did upgrade. But this was in part based on my ability to sell my Z3C for a good price and acquire the Z5C for a good price. For me the upgrade is worth at least $200-$300.
If you upgrade I think you'll find a lot to be happy with. Lots of major and and more subtle improvements, which I talk more about here:
I've been going back and forth for a few weeks now.. I previously had the Z3 and a Z3 Compact.
I ordered from Amazon and it's scheduled to be delivered tomorrow with Amazon's Sunday delivery.. I went with the black version and will report back after it arrives. I loved the size of my Z3 Compact as I am not a fan of the larger phones. Heck even the regular Z3 was a bit to large for my liking,