When choosing comps for your home, I would use 20-25%+/- the square footage of your home. I would also try to stay with in one mile of your location, as well as try to find similar style and function homes with roughly the same year built.
That is the ideal situation but in New England it can be easier said than done!!
$0 - $250K $461/sq ft
$250K - $500K $604/sq ft
$500K - $750K $532/sq ft
$750K - $1M $715/sq ft
Over $1M $469/sq ft
Quite the range of costs per sq ft. If you start looking at waterfront vs non-waterfront, or more desirable areas of town you will get vast differences.
So the short answer, price per sq ft can be helpful in comparing properties but you need to make sure you are comparing apples to apples. Your best bet is to ask your realtor to find you comparable properties to one you may be interested in and compare actual sales price. If the properties are of similar size then you can make the comparison more accurately.
Hope this helps.
You can run reports to find info discussed above on the reports tab of my website