Blending our posts, I go along absolutely with your analogy (saxophones), but also I think the E flat alto horn, the B flat baritone, the euphonium, and a sort of conservatively sized bass tuba (or a good sounding 3/4 contrabass, I suppose) is just a little more towards your logical recommendation.
I realize it cuts out more tuba players (with probably the collegiate invention of the tuba quartet having the specific purpose of involving tuba players in more chamber music), but one of the (sound) problems (at least, to my ears) with the tuba quartet thing is an actual tuba sitting on that third part playing up in the staff or on top of the staff, which often results in bad balance, due to that tuba range being so resonant.
John Mueller, I've mentioned, has put together a quartet for playing some little jobs around Memphis in tap rooms and beer halls. (LOL...Only one of the four of us is young enough to not be on Social Security and Medicare.) I suspect now that he's retired from both Pershing's Own and the University of Memphis, he's looking for some place to play. (bravo!)
During our first reading of some music (along with recording several German things to send out to tap rooms and beer halls in Memphis), I brought a small contrabass tuba, because that's what he had first thought he wanted me to do (was to play the bottom part)...but he changed his mind. I had to sort of whisper on that instrument to properly blend (3rd part) and not be too loud playing the least important of the four parts.
Yesterday (our second get together), I brought the F tuba and there was still a little bit of that same thing (me finding it necessary to sort of back way off and play in the sound - unless suddenly I had something other than harmony). I've mentioned it before that sometimes I use a Doug Elliott contrabass trombone mouthpiece in my larger of my two euphoniums. I can still make it up to a B-flat with that mouthpiece, but it gives me more access to pitches below the staff. I'm thinking that if we have some more rehearsals and reading sessions, I'll probably still bring the F tuba, but I think I'm also going to bring that euphonium with that mouthpiece.
I think there's a reason why Winston used Miraphone rotary euphoniums (as opposed to the English style compensating instruments that his students surely owned) at Tennessee Tech. There are more highs in the sound (Miraphone rotary) and it probably nudges the corporate sound more towards the type of sound that I am hinting at preferring.
I understand the importance of involving tuba players in chamber music in college, but I'm more speaking to moving the sound of this ensemble to something that's easier for casual patrons to interpret with their ears in regards to paying gigs (and no, I don't expect these gigs to pay much.

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Lederhosen:
Those that I had 45 years ago were long ago donated to Goodwill or something. I can imagine that ending up being some sort of semi-significant expense...
OH... I never addressed why I think the bottom/4th part should be played on a smaller size tuba:
It's because that part also ends up playing the melody sometimes, and it needs to sound clear, and not "foggy".
bar gigs:
Don't play too loud. People like to talk.
Put out a clear sound. People like to be able to interpret what they are hearing and recognize familiar tunes..