I'll probably stick with 14.04
I'll probably stick with 14.04 as I'm more interested in using my computer than in playing with the latest toys. I like the Unity desktop, and I think the current version is very polished and easy to use and I have no problems recommending it to anyone.
As for the applications, there's no need to upgrade to get the latest Firefox, as that gets upgraded automatically in 14.04 whenever Mozilla puts out a new version anyway. If you need (or just want) the latest version of some other application, then I suppose that could be a reason.
The desktop version of Ubuntu is what gets all the publicity, but the server version is quietly getting a lot of effort put into it. Ubuntu is very popular in the cloud market, and there are a lot of new things to be found there, like new versions of OpenStack, Docker, MAAS and Juju, and better ARM64 and POWER8 support. The new kernel also apparently has improvements in the file system, networking, security, and virtualization.
As for what they are doing in mobile, I think they are aiming primarily at what they see as the next big thing, which they call "converged devices". That is, they think that as phones become more powerful, they will replace desktops. The idea is that you will be able to drop your phone into a dock and use it with a monitor, keyboard, and mouse. When you are using it as a phone you get a phone UI, and when you are using it as a desktop it automatically switches to a desktop UI. The two UIs are related, but not the identical.
Microsoft is trying to switch to this strategy after the "phone everywhere" concept flopped (Windows 8), and Apple seems to be trying to slowly evolve in that direction as well. I don't know if Google has a strategy for this with Android, perhaps they intend to bring Android and ChromeOS together somehow.
All in all, I'm quite content.