Just the streaming component is worth no less than $8-$10 per month, so this benefit alone is $88-$120 year that their competitors charge.
Add to that 12 books that you read for free, say the books they are willing to let you borrow for free are anywhere from a buck to $10, so that's another $12-$120 extra per year you are not paying.
Add to that the 12 books you are entitled to keep through the Kindle First program. Once a month Amazon offers you four new releases, you pick one for free. Those books usually retail for $4, so that's another $48 assuming Amazon always offers you one book per month that you may want.
So that's over $200 in value without even touching shipping. And the way I use Amazon, if it isn't perishable, and I don't need it right this second, and Amazon sells it a penny less than what it would cost locally plus sales tax, I order it through Amazon and I don't upgrade the shipping.
Hell, my treadmill would had cost me $101.99 to ship (the box weighted 300 pounds) if I didn't have Prime. That's just one lousy purchase justified the price for the whole year. Amazon sold it to me for $261 less than what the non-Prime seller wanted.
$100/year WHEN YOU USE THE SERVICE A LOT is nothing, and this is the first raise in price since the program started.