I've been trying out this vegan thing a lot, and I've noticed quite a few nice things about it: You get to pet Diggles You get to watch animals fight each other to the death while still maintaining your Aura of Self-Righteousness Eelies, Wyrms, Fish Paladins, and Octos do nothing to you-- some of the most annoying ranged monsters in the game! You don't have to deal with Hungry or Thirsty Diggles You get tons of health early game to throw at your enemies Free Tofu! Cons: You still don't get to pet Mustache Spirits
Oh god... In descending order of awesomeness... No aggro from animals. Bonus HP Cure status effects Stunning procs on defending and attacking Bonus righteous damage Free food (and booze if you have alchemy) Nimbleness and burliness boosts Rather overpowered really. The downsides are bad, but can't be made any worse without making Vegan something like Burgulary or the old Fungal Arts, extremely powerful but quite annoying. Almost every build can benefit from it in some way and it holds its own very well, too. Every time I've beat dredmor it has been with a build that was Vegan.
I used to be pretty iffy about the Vegan tree, but after playing it some more I have grown to really love it. The food penalties are actually not bad once you get the Level 5 Vegan decursing skill. I can still chomp on some omelettes before a monster zoo, eat sandwiches, etc. The same goes for animal mobs...I just whack them all and then decurse. The bonus and is also ridiculous. I max out the tree early game and run around with 100 HP and super health regen. Traps are no longer a problem, and neither are monsters, even on GR. The only drawback is you have to be a little careful early game until you get your first few levels. But I think not having to deal with Ocotos or Eelies is already amazing enough.
Once we can pass through our animal friends I will be more inclined to use it. I am contemplating adding it to my melee character in attempt of beating Going Rogue for the first time; as stated those bonus stats and LVL 5 Vegan Cleansing is pretty hard to pass on for a melee character.
In my current game I have Unarmed, Killer Vegan, and Necronomiconomics. The curse dispell works perfectly with the Necro debuffs. Also, I found a Cloud Formations book and now my enemies are almost always confused, blind, or stunned. Fleshsmithing has added some nice hp regen too.
You forgot that Vegan can also be used to create the most challenging build in the game: the Vegan Vampire, with which I cannot clear DL1. If you're feeling nefarious, Vegan works well in the early game with one extra level in fungal arts, since your summoned slime can kill animals with impunity and they wont fight back (works best in No Time To Grind), since you don't even end up missing out on all that XP, meaning you're at normal level with all those tasty, tasty Vegan buffs.
Vegan is neat. Reminds me of the mandatory-conduct-heavy roles in NetHack (Knight and Monk). Both very powerful in their own ways but the tradeoffs in conduct made it somewhat balanced.