Okay, so in order to implement a true SOI campaign, you'll need to do some clean-up on the database, but that doesn't mean you have to wipe it out.
First, here's an idea to deal with the 2500. If you have email addresses for them, I'd do a little virtual tour or photo show of something cool that would appeal to most people - like photos of the first snow or something - and just send it out to everyone with a short note. You'll get back tons of rejects which you can delete from your database. You might get some nice comments as well. Anyway, this will help trim the list a bit. If you don't want to do a photo show, you can just send out some sort of generic, but interesting email - maybe even a Happy Thanksgiving one or something.
Second, I'd probably sit down and start from scratch building your "true" SOI. Make a list of everyone you know and carry a notebook with you at all times to record more names as you think of them, or meet new people. Make an effort to meet new people, without sales pitching them.
At the same time, go through your list of 2500 and create a group for those who you have no idea who they are. No reason to get rid of them, but neither do you need to spend much time or money there. Your SOI consists, not just of names on a list, but of 'EVERYONE WHO KNOWS YOU AND KNOWS THAT YOU SELL REAL ESTATE.' If you have no idea who someone is, chances are they don't know you either and aren't in your SOI.
So, at the end of the "day," you should have two or three lists - one of your true SOI - that is, people you know and who know you and another of names from your database that you don't recognize. The third list, if any, would be people from your database whom you vaguely recognize the name and think they might know who you are.
Once this is done... check back and we'll go from there!