I don't see anything in the RAW about secondary senses or making less sound. Probably (just now remembered it), the +20 is referring to noticing a stationary invisible creature (knowing that one is nearby), and +40 is for pinpointing its exact square.
Altho the RAW does not actually say "cannot see you", it does say this about Total C/C :
Total Cover (definition, RAW) : "You cannot draw any line from your square to your target's square without crossing a solid barrier"
That to me means you cannot see *any* portion of the target, because every portion is blocked by a solid barrier. Total Cover is being behind a box much larger than you, or around the corner of a wall.
Total Concealment (definition, RAW, paraphrased) : You do not have line-of-sight to the target
If you don't have line-of-sight to it, you can't see it. Total Concealment is being far enough away in a thick fog so that no part of you can be seen.
Since Stealth checks are only made when a creature might see you (RAW), then if they can't see any portion of you, they don't get a S/P check to see you. That's not explicitly stated in the RAW, but is a logical conclusion of the rules that are stated.
Thus being in Total C/C is better than any bonus you might want give to a Stealth check because you want to think of being in Total C/C as being "invisible". To my mind, there is no S/P check to make, so what's the point in giving it a bonus?
Cheers!