Sorry to say, but I think Bruce is far from worn out.
As we all know his voice deteriorated badly during 1988-1993 roughly, and that was due to the ravages of too much constant touring. His voice was basically ground down, and plus he had some health issues with it (see 1992 Donnington performance of Hallowed Be Thy Name and you will even see Bruce coughing above the drum kit during parts of the song after struggling to hit the higher registers).
Take his performances from NPFTD and FOTD and compare those performances to BNW (and let me say when I bought it, and listened to it for the first time, my jaw dropped, it was a true return to form imo). See his performance on Nomad and The Thin Line Between Love And Hate and then imagine him doing that back during 1988-1993, there's no way he could have done, even in the studio (where he *should* be able to do it given he's standing still and can control his breathing more).
Another example is his performance during Run To The Hills on RIR. During the chorus, instead of dropping down at ".. for your lives!" like he did for a good decade before, he sustains the note and raises it like he is supposed to. Of course, this is not to the level of the original studio recording, and that of course the likely outcome in a live situation when you're 50!
There is a texture (or lack of clarity) to his voice which I think has come simply with age, not so much as him not being able to sing at a great level anymore. DOD (the title track itself) doesn't go well with his voice imo, as several sections of the song are condensed and feature quick fluctuations in pitch which I don't think is a good skill of his. Bruce's beauty of skill is in "sweeping arias" (highly evident through POM through to SIT and even onto SSOASS despite his voice problems on the album).
If anything, I think he is more controlled and more skilled with his instrument. I think he could quite possibly pull off Total Eclipse now in 2006. He knows more about his limits and his creative ability and I strongly believe that this is evident on both live and studio recordings since 2000.
Cheers H