Good points to keep in mind. However, in my case I have to have a mobile hotspot for my laptop, anyway. And the 4G hotspot I use is much, much faster than the 3G performance of the iPad. Thus, a 3G iPad is redundant and another data plan, even the start/stop $30 per month iPad plan, is an expense I don't incur. Nor, of course, did I incur the $130 initial price difference in the cost of the iPad with 3G. (Much the same reasoning applies to those with smartphones that have a tethering capability.)
The comparative battery life is a valid issue, as well. But frankly, I've never encountered a situation where the (at most) three hour difference between the battery life of my hotspot and the iPad was an issue. Keep in mind that using 3G on the iPad is a battery drainer, too. And for those whose smartphones support tethering, the battery advantage of the iPad may not exist, at all.
For me, the biggest downside is the absence of GPS on the wifi version of the iPad. As noted above, it doesn't matter that much to me because I have superior GPS functionality on my Android smartphone. But even if that were not the case, there are GPS solutions that interface with the iPad via wifi or usb for a bit over $100. (I recall a review of the options on this board.)
In short, there isn't a one-size-fits-all answer to these issues. For many, probably most people the 3G iPad combined with the pre-paid monthly data plan is both less expensive and offers greater functionality than the alternatives. But that strategy doesn't apply to everyone.
