After reading this thread here are my thoughts:
If you have a iPhone, do you really need to tether your laptop using your iPad. It is kinda of redundant. The only case it would be practical, is if your constantly on the phone and you have Verizon or Sprint; if that is the case than a cellular version makes sense. You need to be the person that is constantly on the phone while doing work on their laptop tethered to the iPad at a coffee shop, hotel or remote location.
If your using your iPad (your iPad is your laptop) excusively for remote work and can't lose internet connectivity for 1 minute (can't be bothered to tether to your iPhone), than a cellular makes sense. If your on the road allot, the redundancy of iPhone and iPad with cellular would make sense. If your iPhone dies, switch to the iPad with cellular, or vice versa.
Has for GPS. Do you really need GPS for the iPad? In a majority of cases, the iPad will be able to find your location through wifi. It works accurately most of the time. Would you really need to use your iPad for navigation when your have your iPhone.
If you have a basic phone, then the iPad with cellular makes sense. A iPhone and iPad with cellular is a bit of overkill for the majority of people. There are people who do need both (they are usually traveling at least 50% of the time or work at some outdoor remote location), but most people don't travel as much.
So please save yourself some money and don't optimize for situations that you don't normally encounter. If you truly need the cellular version, it will hit you in the face, and you'll will see no other option.
Thanks
"Premature optimization is the root of all evil" ~ Knuth