Someone said:
since my characer has only two powers, and can use them at will, it´ll be better if we clarify something about the Baleful Utterance power. It duplicates the shatter spell, and at this point I can blast an object with a weight of up to 10 lbs.

uts on his Rules Master hat:
PHB said:
Alternatively, you caN target shatter against a single solid object, regardless of composition, weigh up up to 10 pounds per caster leve.
So the rules seem to make pretty clear that you can only affect ONE object with the secondary use of the spell which in its entirety must way 10 lbs/caster level or less. The issue with the spell (and I agree that it leaves some room for discussion) is that you have to think of this in D&D terms, not in RL terms. I think it's easiest to explain this taking each of your points seperately.
Someone said:
-Can I use it to blast part of a larger, homogeneous object (like 10 lbs out of a rock that weights a ton?)
Thinking about this in real life, you might think that this would be possible, as a brick wall or a ship's hull is indeed made up of smaller objects. This is not the case in D&D terms. In D&D, a brick wall is a unit, with hp assigned to every 10'X10' section. You can't affect a smaller unit than that, and as a 10'X10' section of brick wall weighs a lot more than 10 lbs, I'd say that you couldn't do this with the spell. If the spell could cause hp damage to objects only, I would allow it, but as it is written you either destroy the object entirely, or not at all.
Someone said:
-Can I use it to destroy objects firmly attached to large objects -so they are normally considered part of them- , but that can be safely removed with the appropiate tools or are not homogeneous with the rest of the object (like the lock in a door, an axe´s handle, an iron spike embedded in rocky floor)?
If the object is completely seperate and weighs less than 10 lbs., I'd say yes, you can use the
Shatter spell to destroy it. If it take tools to remove it, I will say that it is not seperate. A padlock on a chest could be affected, a built in lock could not. And before you say it, yes, it's arbitrary, but unfortunately DMing involves making a lot of arbitrary decisions. Remember that if the axe you mention is held by someone, it is considered an "attended object" and therefore gets to make a saving throw (using the holder's save). Remember that D&D is pretty free-form and ambiguous until it enters the realm of combat, and more specifically doing damage, and then it gets really, really detailed and specific. In general, non-combat uses of any spell can be adjudicated much more liberally than combat uses.
Someone said:
-Can I destroy parts of objects mechanically attached to a larger body (like a chest´s lid)
I believe I dealt with this above; no, you can't.
Someone said:
-Can I use it to destroy part of items that, though they are considered to be one object are really composed of smaller, non joined objects (like destroying a single link in a chain without having to blast the other links)?
Only if you do it at a very dramatically appropriate time
If this admittedly conservative interpretation of the ability nerfs it too much for you, feel free to choose another.