As the organizer of the event, that's a decision you have to make. So you have decided to allow your real estate investing business to take a big mailing list step forward and start marketing with proven yellow letters to consistently get new leads. Your leads are just as important as your letters. The best designed letter with a less-than-stellar mailing list will not yield strong results, just as a poorly designed letter with an excellent mailing list will not yield strong results.
The key is to use a strong letter AND a strong mailing list. You may be tempted to try cutting corners by doing the letters yourself or by mailing list purchasing leads from a cut-rate vendor. Yikes. Before trying a discounted method, ask yourself this. When was the last time you achieved breakthrough results by doing something halfway?
Yellow letters are an investment, and it's better to do them correctly to get those breakthrough results than to do them on the cheap and end up in the same place you started, minus your investment. This means you need to identify the best mailing list leads for your purpose and send those leads an appropriate yellow letter. Send your letters to leads that are not yet public knowledge, and you'll get an even higher response rate.