I started a new profile and decidet to test a hypothesis, namely, that unlocking content actualy makes the game significantly harder. I've decided unlock / spend money on only the moronicaly broken stuff, and so far it's been going swell.
So far I've unlocked the following, and for the following reasons:
God's
TT and GG. I don't plan on unlocking any other god, as it's not worth it, excet Pactmaker maybe. GG is a piety farm in any hard or vicious dungeon where there are enemies with poison and you have halpmeh, and TT is the best god in the game bar none (while not being obviously broken like GG, or Drac). His piety loss after you get poison is insignificant, you can buy his piety with money (and recycle), his potions are quite nice - he's very damn usefull, and once you have poison and dodge, easy to farm up piety with and get use of all your potions once you get enlightenment. If you've also been thorugh GG's leveling boot camp, he seals the deal. Any other combination of gods doesn't come anywhere near this. I'll get all of them in Gaan'Telet and Naga City anyway, and I guess I don't need any other combo anywhere else.
Classes
The four basic ones, obviously, and I also found tinker. This is great as the Thief is broken and takes no investment, and Tinker is even better if I ever need scumming runs. The justification for the rest of the stuff is as follows:
Rogue, Assasin - for the gorgons and bandits, to ensure cheap fodder. I probably didn't need Assasin as I get TT's poison in every run (plus the 10 gold from it), and having the poison glyph around reduces my chances of finding Halpmeh, which in retrospect is akin to shooting yourself in the foot. I don't intend to actually play the rogue (I've unlocked the Monk, if anything needs completing 3-4 times I have better options), and assasin is one of those options, especially after I unlock goblins.
Berserker - got him for free, and for the locker space. It did bring Wraiths into play, but they are not really dangerous, and are ok fodder for GG. I'm not unlocking the warlord, cydstep is / was broken, but I never liked it, and having it clog up my glyph quota is not worth it. Or having goos around unless scripted.
Monk, Paladin - For Monk, see thread title, Paladin was there as a strong class, for getting Halpmeh and making Monk stupidly broken, and I thought having Dragonkin around was ok, I needed some more magic dmg enemies (as I'm not unlocking mysteria, this makes Berserker more viable when I can use him to get money from quests)
Wizard, Sorcerer - I unlocked sorcerer for the goats (more cannon fodder), and for the 2nd generation quest. Also, if I need a decent spellcaster. I don't intend on unocking Bloodmage (i allready got enough degenerate classes), but i might eventually for the fireball magnet preps.
EDIT, New Classes:
Tinker - Because it's free, and also good for scumming quest subdungeons.
Dragonkin - Because Dragon islest turned out to be only moderately challenging for Monk, Paladin and Thief without junk in the shops, with worthwhile godas, items and glyhs available.
Items - Soul Orb, Poison Ward, Gloves of Midas, Agnostics Collar, Dragonshield. I'll get the trisword if possible (can't remember which quest does what - I've accidentaly unlocked Mana Bead thinking for some reason that the quest would give me Elven Boots -.-') I've lockered The Collar, Dragonshield and Sensation Stone, every other item in the game except the trisword and fire heart pales in comparison (and I'll probably locker the heart as it breaks spellcasters, as I most probably won't need the collar).
I won't bother looking for the which, if youre not screwed over by balanced content messing up your game (in other words 80% of the stuff that I didn't unlock and probably won't), you don't need whoopaz, or any other potion messin your shops up. I'll do everything with monk first, grab all the money along the way, then mop up everything else that needs no unlocking useless (erm, balanced) stuff with thief, paladin, assasin and sorcerer, then test the fighter in vicious dungens without the need for wasting enormous amounts of time and gold scumming for all the stuff neccessary to have a shot at being competitive.
MISC:
Alchemist: Lvl 1 - i never prepared transmutation, and if I have TT in the game I can ussually buy just about anything.
Bank, Blacksmith - Lvl 2 now, I'll try to get them as high as they go. Again, with TT I'm not really having any money problems.
Bazaar - I'll have to think about. Prepping quest items increses my chances of getting the worthless bead (curse you blue bead!

EDIT:
Having useless but exensive crap instead of the gloves, blood sigil, troll heart and such makes the game much harder. If you think about it, getting all 3 is almost as much CP as a conversion scroll (215?), and all that for around 30 gold, and you can pay a part of it back with gloves, AND you can get 7-11 extra HP off of troll heart.
JUSTIFICATION:
I actually had an easiest time ever completing the Dragon Isles with the monk this way. Preps? Conversion stone and scroll, subdungeon, altar scouting, +10% badge, 35 gold. Found GG and a lvl 4 snake, had absolution at lvl 2, converted to tiki tooki before I uncovered half the map, mopped the floor with the bosses. Guys, these things ARE broken, I've unlocked only 2 gods and found one glyph, and that translated into more than 200 piety on a deity that's considered "stingy" - before I uncovered one third of the map! I whish I'd done a video of it.