They will be more receptive to your presentation and product offering. They have credit and have paid you in the past. Think about this for a second. You're a farmer, and you need milk. You wake up and decide to go milk your neighbors cows.
Sales is the same.
They're waiting for you, dripping with business. I don't think you could ask for much more than that. It beats a cold call by 1,000 to one. Your enthusiasm will set the tone. Enhancements and upgrades have kept the computer software industry profitable since it's inception.