KeyBee,
You make some great points and defiantly good things to consider. I'd have to also think that if you are going through all that trouble to personalized your letters you must be running a low delinquency. If not, then this effort would be costing you time and money. I'd have to admit that I'm a bit skeptical about the idea that personalizing a late letter lowers delinquency. Personalized or not, the customer is late and needs to be notified and this central mailing idea is a great one.

I go through less paper, don't have to keep a stock pile of stamps and the service costs me no more than the price of a stamp. I call that a win win. I'd rather deal with a few calls from late customers who got a letter after making a payment than not sending the letter at all. Such letters serve as a great reminder that they need to pay on time.

With central mailing I choose which types of letters are mailed centrally and have reports that allow me to monitor what has been sent. It's a great feature well worth giving a shot.