a few things to consider:
-Field of view.
Bigger magnifications means you are looking at a smaller chunck of the world. You need a low enough lowest magnification to work for YOUR hunting conditions. For some this may be 3x, for others 4x or even 6x would work.
Once you have your bottom, it's simply a matter of using your dollars to best suit you needs. If there was a 3-9x scope and for the same price you could buy a scope of equal quality that was 3-12x having extra zoom isn't going to hurt anything. Heck, 2-12x would be even better!
-Value for your dollar.
If you are going to spend $200, you want a 3-9x 40mm because there is an economy of scale that goes with this popular choice. With $200 you can get a very good 3-9x for cheaper than you could get the same level of quality 2-7x.
The difficulty of crafting a great lens and properly building a scope goes up as magnification increase. A $200 3-9x 40mm can be a very good scope. A $200 6-24x 50mm is most likely junk. What's really sad is I just opened up Midway's scope page and sorted variable scopes by popularity, a 6.5-20 x 50mm 'simmonswhitetail hunter' is currently most popular...for $100. If you are doing 20x, a $100 scope probably isn't going to cut it
I don't think it's a case of needed or wanting too much power that hurts, it's wanting too much power and being unwilling to pay for it.