I will preface my response by saying I haven't read all comments yet, but I will and may have more to say later. I use my B string ALL the time, but MUCH of the time it higher up the fret board. As for the low D, C, B area sounding muddy; that isn't a fingering or playing problem (mostly). That is a sound system problem. Low B is 30.87 Hz. Not many churches will have subwoofers tuned that low. Most bass cabs aren't tuned anywhere close to that. From my experience, 50-60 Hz seems to be standard tuning for bass cabs.
As a designer and builder of many home audio, car audio and live sound subwoofers, I can tell you there are many differences. However, to hear the fundamental low B0, your cabinet must be tuned around 30-31 Hz or at least on the lower side of the 30-60 octave. Can you get 30 Hz from a cabinet tuned to 60 Hz? Well...yes, but because the woofer will "unload" quickly below the tuning frequency. I often see bassists referring to their speakers "farting out!" That's the sound of the pro-designed woofer unloading, and that will sooner or later damage the voice coil. In a subwoofer designed for pro use, the same thing can/will happen if pushed too far. If they aren't being pushed that hard, the sound produced will simply sound "muddy" because of the overly-flapping woofers unloading below their tuning frequency.
Along with my 5-string bass, my Aguilar TH500 head, and my many top cabinets; I have an 18" woofer in an 8 ft3 cabinet tuned to 30 Hz powered by a 1500-watt RMS amp. My system sounds very clean. I've never been accused of it sounding muddy. Since my 18" cab is tuned lower than many subs, often the sound coming through the subs must be reduced or rolled off because THEY sound muddy when I get down on those lower notes on the B string.
Some people have referred to using a high-pass filter. I even saw 50 Hz as the suggested frequency. Well, it depends on what slope the filter is set at; but if it's a 24 db/octave filter set at 50 Hz, that means your B fundamental frequency will be down 20-24 db below the 2nd harmonic. Many people are happy with that sound, and that's OK if you choose that. I, personally, don't like missing the fundamental. That's why I have my system that many will think is overkill! It's all personal preference, so I just wanted to give you my 2-cents worth. We ALL should enjoy what we do! That's the best part! Don't sweat the rest!
BTW, those that say playing on the B string gets into the range of the kick drum must be playing with a VERY poorly tuned kick drum in the mix. A properly tuned kick drum will resonate around 60-80 Hz on the low end which falls right in the middle of the fundamentals of the A & D strings on bass. That's why a lot of bassists like to use some low-mid emphasis to "punch" through the mix above the kick drum. However, if you can use the fundamentals below the kick drum and if there is proper subwoofer sound support, you will not blend in with the kick drum.