The marketing mantra is that the money is in the list, and this is true and has been so even before the Internet came to save the leather on the marketer's shoes. However, by now I am sure you are aware that the wealth comes from inside this list. This is where the relationship that you have with the members of your list can be found. This relationship takes time to develop and along with generating an honest and open narrative with your list members, you have provided consistently good advice with beneficial links for free. Through this you have generated a community built upon trust and expectation.
However, if you were to buy that list, then you would need a quick return on this investment and not just to recoup the money it cost to gain these personal details. When was the last time you changed your email address? In the US, about a third of people mailing list change their details every year, this means that you cannot afford to sit on a bought mailing list for too long. An undeliverable email is akin to putting the cash straight into the bin. Even if these people do receive your email, you could still find yourself in trouble because if they do not understand why they got the message from you then they may provide your details to their ISP, and thus you may be added to the ISPs' spam filters.
Since social media came to prominence in everyday life, there is really no need to make this mistake. Always ensure that this email campaign is a planned stage in an overall marketing campaign, perhaps even announcing that certain lucky people will be receiving a message on a specific date. This is of course a great method to increase interest in your offer, but you could always use this interest to capture personal details for free on these same social media sites.