Data exchange rate; what's your's worth?

On Sunday, I commented about plans that Facebook may have to sell data about our activities as endorsements to our friends and family.  I expressed the concern that something I read (or listen to or watch or whatever) but don't necessarily 'like', is taken in and of itself as an endorsement by me to my friends of either the content of the item or of the publisher of the item or both.  

I also said that I have no major objection to friends seeing most of what I do online but there are times when I would prefer they didn't.  It is not just that there may be sites I prefer they didn't see I had visited for embarrassment reasons (like Doctor Who, for example) but there are also competitive reasons why I would prefer my approach to knowledge gathering not be disclosed to everyone who knows me digitally.  Since Sunday, I have refined my thinking a bit 

My clarified concerns - if Facebook implements this plan - are divided between the credibility of endorsement and its value.  

So first, it doesn't seem to matter whether I actually 'like' something; apparently I can still endorse it.  That just doesn't sound credible and I think my friends will see through such endorsements. 

Second, if I endorse something, I want to be clear what it is I am endorsing and why.  If I really want to endorse something to my friends, I want the endorsement to be helpful to them.   

Third, isn't what and how I endorse something quite personal?  Not private maybe, but personal.  I am not sure it can be done by proxy.

Finally, and most obviously, endorsement has value - or Facebook couldn't sell it.  But, is whatever Facebook gets for my endorsement (over and above what it already gets for my other data) still within the overall value of Facebook to me?  Looked at another way, as Facebook earns more and more out of my data/data about me (delete as you think fit), do I get a corresponding increase in value out of Facebook?  

I am not sure I know the answer or even that I have the faintest idea now how or even if it can be calculated; I am also not sure that I will spend too much time thinking about it but I suspect it is the kind of equation we may all need to think more about in the future.  Platforms like Facebook - and this clearly isn't just a Facebook issue - will come up with ever-more creative ways of 'monetizing' user data and we will need clearer ideas of what we think that data is worth to us.

Data is like a currency without an easily calculable exchange rate; what's yours worth?