It's a whole lot more valuable to have 1 000 potential buyers than 10 000 prospects. And what is the difference? How you attract your subscribers. Do mailing list you step over anything to get the persons contact information, or do you give them the impression that it is lucrative to be on your list? If you use the last strategy you probably don't have as many people on your list, but you will have a very different quality on your list.
They are more likely reflected people not desperate just to make a few quick bucks. If you attract these kinds of subscribers and treat them well mailing list you will develop a great friendship and loyal customer-base for years to come. I am on a number of e-mail lists (35-50 haven't the exact number) because I can always learn new things from them.
But I can tell you that about 75-80% of the e-mail lists I am on NEVER provide anything of value, they just try to sell me stuff and some of them mailing list with no ethical standard's at all. Some of them send out several e-mails every day and NEVER give out anything of value. I don't know about you, but I would never consider to bye anything fro them.