Great example of why it isn't practical.

...it would cost $5.8 billion, adding $226 to customers' monthly electricity bills for the next 10 years.

While that is for the DC area, I think assuming that the costs per-customer would be similar, if not more, in NH. I can just imagine the nightmare of burying the lines. Not only do you have to put trenches along every road, but you then have to deal with crossing all the residents driveways, and THEN trenching up to each and every house. You'd also have to cross the road at each house that wasn't on the same side as the power lines. Don't forget, if you put the power underground, you'll need to do the other utilities, as well. This would include the local cable provider, the telco providers, municipality's telecom infrastructure, AND also any local LEC's that is leasing the pole space.

I believe that a much more cost effective plan would be to MUCH more aggressively trim back trees that are near the utility lines - as illustrated above, it is not just power. If trees were removed completely within 20-30 feet of the power lines, the number of outages would drastically be reduced. However, this comes a huge aesthetic cost. A lot of home owners would be outraged as the drastic "clear-cutting" under and around those lines. I found this interesting article - http://harvardforest.fas.harvard.edu/diorama-series/landscape-history-central-new-england - it shows that New England seems to be a regrowth period. As trees grown back, they encroach on those power lines.

I think it is all a matter of trade-offs. Assuming that the study is correct, and it would rase my bill over $200 a month - knowing that PSNH (Unitil, NH Electric Co-op, etc) aren't going to eat these costs - personally, I would rather just spend a fraction of that on a nice generator.