I have actually discussed this topic with a lot of my black friends because I wanted to understand it for myself also. I wanted to understand their point of view on this issue….After discussing it with them though; there are definite differences among generations… The older black people I’ve spoken with don’t like the word at all due to this reason you quoted:

Many older black people argue that the change in pronunciation is not enough to successfully separate the word as young people would have it used from its older, more offensive roots.
Of course this is understandable… but the younger black people that I know view it this way stated below:

Nigga is often used synonymously with, and in the same sense as, other less controversial slang words such as dude and guy.
"Niggers was the ones on the rope, hanging off the thing; niggas is the ones with gold ropes, hanging out at clubs."
After discussing it at length with many of my black friends I have come to this conclusion which you quoted:

"Nigga," if one considers it as an entity separate from "nigger," may be even more complex in usage, because generally its use as an endearment or an insult is dependent almost solely on the listener's interpretation when spoken to.”
This quote pretty much sums it up... there are so many subtle nuances and tones in which the word can be interpreted that a person has to tread very carefully. My black friends would actually have no problem if I were to use the word in this sense,
"what up my niggas.”
But if the phrase is switched up to
"Hey you niggas"
then they might look at me kind of funny simply because of the difference in phrasing and tone..
But they accept the former solely due to the fact that I am Hispanic and so it sort of works in a 'quid pro quo' kind of way.. I am allowed to use the word with them in a friend kind of sense and they are allowed to use nicknames referring to Hispanics. It works this way out here because Blacks and Hispanics out here can relate to each other on a sort of “minority level.” They say that white people are not allowed to use it with them at all though. (friend or not)

But it gets even more complicated because this applies only to the black people that I know.. I would never attempt to say this to a black person I didn’t know.. Even if I heard them use the word casually.. As far as the other form of the word which ends in “er.” They say this is completely off limits for everyone.. I would never dare use that form of the word even with black people that I have known for years. It would probably result with me getting punched in the face.

My black friends have provided me with these established rules:
1. I can use the version of the word ending in “a” with them in a 'quid pro quo' fashion. (applies only to younger black males that are my friends)
2. The version ending in “er” is completely off limits.
3. For white people the usage of either form is off limits for them.