There is no right or wrong. Its up to you. But if your having trouble making up your mind, I would judge it by the effort to convert your list into sales. So if for example you have to talk to people to convert the sale, I would want laser precision as I don’t want to call every man and his dog to find out if they are a real prospect. But if it can be done automated online, then why not have a big net catching everyone. but be warned, and open invitation for a wider audience usually puts off the real prospect, who is looking for someone tailored.

A good way to find out your market is to look at google keywords tool. You can still make a lot of money homing in on a small niche.