Re: cello resonance, sympathetic vibrations and so on, yes the reason I am woodshedding the bass in 5ths tuning is to achieve exactly this sort of stuff...and yes, I like the zound very much.
And no, I can't demand exactly the same thing of the bass in 4ths tuning. If I try to follow those same "markers", I end up getting a little lost. Sure the open string pitches are the same as the violin, but that doesn't help me a whole lot for some reason. Maybe it's because I'm hearing things in some sort of hierarchy or something. I don't know. All I know is when I'm playing through scales and arpeggios, I can match open string pitches and harmonics with stopped notes far more often in 5ths tuning.
But the tone of the bass in general is different in 5ths tuning, though the range of notes can be made identical. It's just not the traditional sound to me, and I sometimes wish that didn't have to be the case. Hearing someone like Edgar Meyer do the cello suites in a hall is an experience no cellist can produce. It the bass speaking, and it sounds FANTASTIC.
To me, intonation's just not a simple thing. The best I can call it right now is sort of an ingredient for some musical expression, to give it a taste. The bass in 4ths is an ingredient, and lots of stuff tastes pretty darn good with it.