The value you mention is accuracy - which is not that sought after in the current market. Right now if you create a mailing list for motorcycle owners, which no one can actually use (DMV laws against it) and instead use inferred data - you will get the same response rate as you typically do. It's really up to the analysts. Facebook can gather data, but the question is can they actually leverage it - or will they sell you a data dump? Will it be an external or internal cost? Right now, you can place ads there, but you can't just buy from them a list of names and interests (income, and etc).
In that regard Facebook could at most, right now, give me partial information - name, city, phone number. If they are provided. E-mail would require a TOS change. They don't ask for a street address. So I would then need to do a merge with my existing consumer database and find out where John P. Smith lives, if I have him, or do I have him as John Smith, no initial.
There is another side to it - that you don't mention, and I failed to - a channel to reach consumers. Facebook, beyond interstitial ads, could be the mailing address, the inbox, etc for individuals and households you would like to hit. E-mail laws are in place, phone laws are in place (snail mail - forget it - bulk mailing supports the post office). There is no reason Facebook couldn't suddenly turn on a way for someone to send marketing material to users directly.
If facebook's data collection really was no more egregious than current practices there is absolutely no way wall-street would be drowning in their own drool over the company.
I disagree. They are valued because of the user-base and the eyeballs for ads right now - and using the data generically to target ads (they are horrible! I would do much better with a custom list... and probably charge less). They can not learn any more than what Visa is telling Experian, etc. Why do you think you have been urged to get that Debit Mastercard? The credit card companies, and their ilk, the houses who collect, analyze and sell this data - some totally private - are valued indeed. Facebook has yet to be traded in a way to let the market actually decide their value. It's a guess - and it's the internet - it's fleeting at best.
I don't even come to say I support all of this marketing stuff. I was called scum, over and over here - and I take it with a grain of salt and all. I was floored myself when I learned how it all worked - but we have to make money. Creating a mailing list isn't exactly dumping petrochemicals in the river by the playground. In reality, no one looks at the names - no one checks up on people. The lists are actually made to be small - and not to bother people who won't reply (it's a higher cost per contact/response/order/etc).