Hard disagree on this.
1) Whether or not you'd watch other shows dubbed should have no bearing on whether you watch SAC dubbed
2) This will depend on the show in question. A well dubbed show will make sure they're working with the english voice cast to capture the nuance where possible. However, I'd argue that unless you speak japanese fluently, you're not getting the "original interpretation" of the character anyway, since you don't speak the language. You're getting the interpretation of whoever did the subtitles. You can get a bit of nuance from tone etc, but you're likely to misinterpret a LOT here if you don't speak the language, and that's always going to be overwritten by what the subtitles say and the personal interpretation of the translation team.
3) I'd agree that most english dubs are pretty bad, but that's not a universal truth. There are a lot of great ones. SAC happens to be one of the great ones. It's daft to say "X, Y, and Z shows have bad english dubs, so don't watch the english dubs on A, B, or C shows".
4) This seems weird. It's a TV show, not real life. The characters speak whatever language the audience is going to understand. Regardless, you're going to be reading the subtitles in english anyway so it's not like you're getting some pure understanding. The only difference is whether the translation is filtered through a subtitle or a voice actor.
5) I can see your point on this, but, to be fair if you're making that argument, there's a pretty obvious counter point that immediately gets raised by having them use different voices. Again I don't want to say too much about for the sake of OP but I hope you get what I'm getting at.
If you prefer the Japanese, that's fine, and if you speak japanese, then more power to you and it's probably great to watch it in the original language, but if you don't speak the language then I really don't think you're getting much, if anything, out of watching a subtitled version. Most shows I'll watch with subtitles just because, like you say, a lot of english dubs are baaaad, but it's not like I'm getting anything else out of it or gaining some understanding that I wouldn't have with a dubbed version, it's just that the english voice actors make my skin crawl.
With more complicated shows, and I think SAC and ghost in the shell in general fall into that category (without meaning to sound too pretentious!) I do think there's a fairly good reason to watch a dub, so long as it's done well, just based on it being easier to follow. Comprehension is generally easier for people when they're listening to someone talk rather than reading words (especially if, as in the case of subtitles, you have a limited amount of time to read them before they move off screen).
The english voice cast are all very accomplished actors, and while I'm sure there's some nuance that they've missed somewhere, I don't understand why that nuance would be gained simply by listening to a language you can't understand a single word of. Let's not forget that you can run the translation subttiles for the japanese voice work over the english voice work to double-dip from the translation pool if you really think there's something to be gained from those subtitles.