The aim of maximizing transparency points toward a possible solution to the problem of spam. The enablers of spam are the companies that sell customer data, which brings them a little extra income at no financial or reputational cost.
Possible solutions to this problem generally involve either forbidding some data exchanges, sometimes with the precarious justification that publicly available data nonetheless somehow "belongs to" those to whom it refers; or taxing the spam itself by taxing all emails, which would be a pervasive nuisance and an intractable enforcement problem. In either case, the value of an individual's privacy is fixed at an essentially uniform level by fiat, rather than chosen by the subject himself.
A better solution would be for the government, in its role as guarantor of transparency, to mandate that sellers of contact information must themselves contact the subject, using the same information that they are selling, and inform the subject of the sale and of the price they received. This would empower individuals by informing them about the paths by which their personal details diffuse about, and would then let data-sellers decide whether the gain was worth the likely affront.
[Cross-posted to Chequer-Board.]