Better Cow(& Mooshroom) gameplay progression

I think the cow progression in this game is one of the better ones, with harder to get cows giving slightly better loot. Unfortunately, they're easily overshadowed by other Minecraft features, to the point where I'm pretty sure some players have never even heard of brown mooshrooms.

In this post, I want to suggest small tweaks to their behaviour that would make them more streamlined and desirable, while not op.

For the purposes of this post, I will refer to them as: cow (Tier I cow), red mooshroom (Tier II cow), brown mooshroom (Tier III cow).

Tier I cow:
Should be left untouched. It's a perfect mix of "useful for beginners" and "useless for advanced players".

Tier II cow:
It should give more exp, leather and beef than normal cows (+addendum at the bottom of the post).
  
Tier III cow:
It should give even more loot. It doesn't spawn naturally, so players should be rewarded for their efforts.
Normally, I'd suggest changing suspicious stews to potions, but since the introduction of the lightning rod, tier III is a little easier to get (I guess that one would be good if ever new cows would be introduced like mooblooms, but I digress), so here's an alternative:

I think Tier II and Tier III should have the ability to turn dirt or stone into mycelium (Tier II spawns on isolated islands so it won't grief worlds), with Tier III also having the chance to create both mushrooms on top of existing mycelium, as this will allow players to build new types of farms with them.