I have never ever bought anything from an email. And I find it so bothersome to click a nice ad with promising title and instead being led to an opt in.
I used an email solely for IM stuffs and have so many spam emails that I don't even know where they got my email.
And even if you have a "list" ,won't they get bored of your constant "product's sale pitch emails". Just my thinking so please don't get offended.
Another query: What will you do if you have a list (1.5k+)of your buyer's paypal email? These are not opt in and can you sell products to them?
Myself my paypal email is exclusive.