Someone on that link I provided said that just like with hotdogs, you don't always want to know what went into your favourite album
Credit-wise, I don't see anything wrong with saying "additional guitars by ____ ______" somewhere in the credits, leaving it to speculation whether it was the entire song they did, or just some overdub corrections, or even the 33rd layer of guitar, while the band member recorded the other 32.
While I already said that it doesn't matter to me very much who played what, I should disclose that I generally program and quantize a lot (not all) of the music I record, and only play live instruments that have strings on them, or synth performances that have too many knob tweaks to be bothered programming that level of detail. But, it's very important to me that
I play those parts that are played, so obviously it must matter to me to some extent (even the thought of someone else programming my stuff makes me feel uneasy). Maybe I have good ethics, or maybe I have low self esteem and just want to prove myself. Either or, it's the same result ;)