I haven't thoroughly read all the content of this thread, but I have a general idea of the direction this is going. However, there are many reasons why people want to own an acoustic bass guitar (ABG). One of them is for comfortable jamming in the sofa. I have a total of four ABGs of different types.
The one that was bought for
sofa jamming is an Ibanez PNB14E, which is actually a parlour guitar which is fitted with nylon-cored strings (similar to strings you get for the Taylor GS mini). It has enough volume to play together with a moderately volumized singer (such as my wife), and plenty of volume to annoy any other inhabitants in the living room where the sofa is located should you decide to jam all by yourself. I find the bass to be very fun and very inspiring indeed. It's also fitted with a microphone should you decide to upgrade your band to a fuller setup (including other instruments and higher volume singers).
For jamming with
a single guitar playing friend and singer, I also have a Morgan AB310, Morgan Guitars being a local Norwegian brand of Asian imports. This is the only ABG that I have ever tested that has a lively tone and enough volume to actually be heard in any sort of acoustic band situation. Measured up against my DB (which may not be the best DB in the world), it actually competes quite well. I have successfully jammed with mentioned guitar playing and singing friend, and even my wife kicked in on the choruses. The bass could easily be heard in this setting. I didn't have to pull the strings off to be heard, either. Again, there is a built-in mic and preamp for bigger occasions for when you want that bronze zing in your bass tone. But beware of feedback, obviously. I wouldn't recommend it for a metal gig. I have tested several other basses of the same exact model, and they have all been very similar to mine, so there's some consistency to this model. The brand's other models fall into the next category I'm addressing below.
The two other ABGs I own (a Johnson and a Samick ABG), as well as the 2-3-4 other ABGs I've owned over the years (a Takamine G-series, Washburn and one that I cannot remember the brand of), are all fun instruments, but not particularly lively and definitely not loud. The seem to be a little confined and less open, and doesn't ring out anywhere near my Morgan above. I tend to think of them as Acoustic-Electric Bass Guitars more than pure ABGs). These basses sound fine enough by themselves, especially with nylon cored strings, but they do need to be amplified to be useful in most settings (apart from the aforementioned "in-the-sofa-jamming-by-yourself-or-to-annoy-the-wife"). That said, they do sound different than electric bass guitars, both due to the acoustic character of the body and the difference in strings and pickup solutions.
Disclaimer: I have not tested any other "expenssive" ABGs from brands like Taylor, Guild, Tacoma, Martin, etc. But the fact that my AB310 works quite well proves to me that it's about making a bass with a responsive structure that actually allows the strings to drive the top into moving enough air to be loud enough. I'm sure Guild/Tacoma/Martin/Taylor/Furch and others will be capable of doing the same. But my clear advice would be to "test before buying".
A lot of people are referring to DBs. The DB is a fantastic instrument, but for someone looking for an ABG, a DB is not a practical solution. for one, it's a hazzle curling up in the sofa with a DB on your lap. And then you probably have to upgrade your car if you are going to gig with it. Remember, for a lot of gigs, you'll still have to bring an amp in addition to the DB as well.... so that makes an even bigger transport load.
Also, a lot of people are referring to Uke basses. I own two (and to be honest, I don't really like them). To me, they do not answer the question with regards to an ABG. It's a different instrument, and it's got rubber strings. If you're looking for an ABG, you're probably not going to want a uke with rubber strings.
So if you want an ABG, I'd say get one, and be aware of the limitations. Also be aware that as a more acoustic instrument, there is likely going to be bigger difference between model, brands and price tag than you are used to from electric basses. Also evaluate whether you were looking for a DB or a uke. If not, keep hunting for an ABG. There are great sounding instruments out there, and some of them are quite useful with regards to volume as well. And miced and preamped, they provide a different sound than your average electric bass as well
Good luck!