Potential creation for a contest here. My concerns:
1. This is too easily broken.
2. Does this need to say "Whenever enchanted permanent's controller activates an ability of that permanent" or "whenever an ability of enchanted permanent is activated" instead of what it says? Cards like Artifact Possession would seem to indicate the first option.
3. Is this okay at uncommon?

I changed it to prevent easy infinite mana with cards like Skyshroud Elf. An alternate version might be better as "Whenever an ability of enchanted permanent is activated, add one mana of any color to your mana pool. Spend this mana only on spells."

To your point 2, yes, it needs to be "a player activates an ability of enchanted permanent". (Assuming you want to be symmetrical with things like Squallmonger, you might then want to update the last clause to say "that player".)

I think it's okay at uncommon. (That is, if it were printable at all.)

­Student of Warfare and other creatures that have ":" abilities say hi :)

Yeah, normally we need to reference cards like Warrior en-Kor to point out the problem, but this does turn every Frozen Shade you control into a powerhouse, eh?

Yeah, I'm giving up on this one. There's no way it can work easily.