The leaves from material crops can only be processed as an ore booster, yeah, but it's just water as the fluid generally. Some of the IC2 material plants simply drop dust or gems, which is useful. You can in theory get an entire field of Olivia plants and never mine Olivine again, but you need an Olivine block for each plant so scaling up is slow unless you have a stockpile of the material in question already. That's the main problem and advantage to IC2- you can scale it up quite well, but it requires resources to do so. Bees on the other hand are hard to scale up but you won't usually need to since only a few material comb types can be directly centrifuged. Combs make great ore boosters though since you really only need Life: Longer and Production: Faster on your bees to get a decent frame-boosted rate of production. Longer lifespan means each queen will go through just over one Untreated Frame in its lifespan so it's easy to maintain. You might want a big cotton field to keep up with the string requirements...
Oh also you can get bees that spread Thaumic Flowers which means you have essentially infinite mercury and blaze powder. That's not all that great though since mercury really only gives you silver and gold, and blaze powder isn't terribly hard to get in the first place. Gold specifically is available in large quantities from material bags, but you can melt down treasure from nether forts for a large quantity as well. Silver is just a common ore. Oh right, mercury can get you platinum as well, but that's pretty easy to get via thaumcraft. You can get the nebrisum and lucrum from mana beans, which scale up easily (but slowly) and can be automated. I haven't found any of the ore types that can be processed with mercury to get platinum, anyway.
