The attraction score hardly matters at all as you are free to throw away creatures until you have to composition you like, and any slowdown this causes usually a smaller negative then building a much larger room. So no matter how you slice it, not really an important topic,...
Beyond that, I don't think it is a more complex concept. Actually I believe they sort of did it like this in DK2 as well,....
Right now, you build a 3x3 torture chamber to attract mistresses,... you'll get one torture device. I would say that building a 3x4 room should give a slightly bigger chance of a mistress, or even a 4x4 room with 4 torture devices. However, in fact you need 18 slabs to increase the score, so even though a 4x4 room is not enough, 2 rooms both sized 3x3 for a grand total of 2 torture devices are enough.
I don't think people would want to build strangely shaped rooms to attract less of a creature kind, but they would build better rooms to get more of the good kinds. Mistresses are a fine example, in many levels a 3x3 room is enough, but building a bigger room to get more of them would be a valid tradeoff.
Simply put, every 'workstation' should attract more creatures drawn to that room type. And if you have more warlocks then you have bookshelves, they should have less interest in joining your dungeon.
As far as I'm concerned the effect may be a lot stronger then it is now. Currently you get your creature composition by throwing out creatures you don't want. You should only be able to do so if your dungeon is really really big,.... I think it would be a lot more entertaining that you have to build a specific dungeon for specific creatures, that you would have to work harder to get a large quantity of the most powerful creatures in game:
- 25 lair, and 25 hatchery, sure you get 2 bile demons. Want more, build them a lot bigger.
- A single dragon might join you when you have a large treasury, but you better stockpile huge amounts of gold if you want more.
- Every mistress better have her own place to get slapped around
- A single slab of barracks? That means you only want one orc.