* Releasing the source code will result in many variants, some amazing and some just too silly.
* The mechanics of the game will be in full view.
I understand why you hesitate to release the source code and I feel for you, but do not feel like your work will be diminished because someone made a silly variant. It won't. We all know who the gave many of us so many hours of joy (too many?). Even today when I play Angband, I ignore all the variants and play the real thing. People know which is the real deal and which is not. Sometimes these silly variants come up with stuff that is wonderful, and that can be incorperated into the core game.
I understand you wanted to keep the mechanics of the game under lock and keep, but this has always been a sore spot with me. Some people get enjoyment from the mechanics (myself being one). I like to optimize my characters using game mechanics. Releasing the source code will not spoil the mystery for everyone, just everyone who doesn't want the mystery in the first play.
If for nothing else, release the source code for the bug fixes alone. I hate when ADOM crashes when ever I create a Skilled character.
Whatever you choose, I would like to thank you for the many years of enjoyment you have given me. All these expensive video games I have stacked behind me do not even come close. What is it that these young kids say these days? "You da man"?