Troubling. Seems to me that there are two decisions. Whether to buy the 3G radio and whether or not to use it.
Buying the radio is inexpensive if one uses it, expensive if one does not, cheaper if one buys it up front, dearer if you buy it late. One really gets only one bite at the Apple.
If one uses 3G, the cost of the radio is a nit, the cost is mostly in the service. However, one can decide month by month as to whether one wants to use it and how much.
Based upon this analysis, buying the 3G radio is a bet that one will use it at least some of the time, and the more one is likely to use it the better the bet. On that basis, I would probably buy it.
However, mine is a special case. I have sunk cost in my MiFi card. I pay $60/mo, whether I use it or not, and an infinite amount if I use it a lot. If I velcro my MiFi to the back of my iPad, I have 3G without buying the 3G radio on the iPad but a higher rate than if I had the 3G on the iPad. If AT&T/Apple will permit tethering, I can drop my MiFi, and after recouping the cost of the 3G radio and the early termination fee on the Verizon service, I will actually save money. So, I have an extra bet that AT&T/Apple will permit tethering, high risk, high reward. This makes buying the 3G radio a better bet for me than for others.
One more possibility, if AT&T/Apple permit tethering at a rate lower than Verizon's rate on the MiFi, Verizon may have to lower the rate on the MiFi. If that were to happen, not buying the 3G radiio and using the MiFi at a lower rate would be the best deal for me. Too many contingencies, not enough money involved, I buy the 3G radio anyway.
Since, I buy a new iPhone every year, I expect I may buy a new iPad every two years. Who knows what rates may be in 2 years. In two years, we may be buying LTE, at least on one carrier in some markets. Even at today's rates, one would get a bigger bang for the buck. It will be worth buying a 4G radio for, a new MiFi or a new iPad. Again too many contingencies and too much time to influence a decision that I must make in the next couple weeks.