How to know how much a lead is really worth?

[lordp]

Giving up free gifts during this time of the year and also doing discount we have collected a few thousand emails which can be considered as leads.

So, here is my query how to know how much each they value and how we can market them effectively?

A lead is not a lead until it gets convert. Its just contact so try to convert them first. Giving them something of their interest or something that they want is always a good idea.