Should I sell my 128gb Wifi iPad Air 2 to buy a 128gb LTE Air 2?

It sounds like you're OK for now, so if I were you I'd wait until the new iPads are announced and make a decision then.

 

You'll end up needing an additional SIM card for the iPad as well. It'll really depend if you prefer using the iPad on the go as compared to the iPhone 6 Plus..

 

I have LTE on both of my iPads. I would not ever buy one that didn't have that function. I'm very mobile and not around wifi all the time and find it inconvenient to use my iPhone as a hot spot. As a matter of fact, my iPads serve as a hot spot for my MBA when working remotely.
I also use my iPads for gps navigation and only the LTE models have that module installed. It is up to you of course, but I find LTE very useful.

 

Just found out my beloved mobile hotspot will be killed by Spirt this November 6 BUT I am glad I still have iPad Air with LTE!

 

I like GPS. So I'll get an LTE version.

 

I have the WiFi only version. My next one will be LTE for sure though.