Any number of legitimate subscribers is worth putting effort in to.

The fact that they have subscribed means that you have or had something of interest to them.

One thing you might like to look in to is setting up some kind of autoresponder so that when someone adds themselves to your list, your server sends out a message every day/week/month until they unsubscribe.

If you setup an autoresponder, realistically, you would only need to setup one round of emails, 365 for daily, 52 for weekly, 12 for monthly and your list is pretty much set for life.

Regards,

Lee