I'm not sure why the switches would be noisier since they are the the same rough construction other than the number of poles. Are you saying the buffer corrects for this?
The difference is that with mechanical true bypass (like a 3PDT), the mechanical switch is directly in the audio path, and in many cases you can hear it--for example if static builds up on one side of the switch, you hear a loud "pop" when you click the switch. With a buffer, or with relay-based true bypass, the physical switch is not in the audio path. The circuit opens and closes silently.
Apparently not in the case of the CEB-3.
Yeah, I don't know
why this is, but Boss, DOD, and other "cheap" buffered brands are a mixed bag--with some of their pedals the buffer sounds great, with others it sounds like total crap. Sometimes the issue is only apparent when you have several of them in a chain. We have to take them on a case-by-case basis.
... if your bass is buffered already by and active preamp and/or a DI, there's no point in having more buffers along the way because you should be able to drive a long signal length (i.e. cable) without changes to your sound if every other circuit is bypassed.
That is true, mostly. Generally speaking, if you have an active bass you don't have to worry about signal loss
unless you go through a pedal with bad-quality bypass, or unless an effect you use has crazy high output impedance. And if you use a DI, then you don't have to worry about
further signal loss
between the pedalboard and the PA. Of course the DI doesn't help your signal going to your amp. And if your tone is dulled by a bad bypass on the pedalboard, then a DI can't retroactively fix that.
One way or another, you're right that an active bass should have no impedance problems with true-bypass switching.