Allright, here goes;
The similarities to your and my situation are striking, actually, so I will share my humbling experience.
I too am a lefty, and have been playing EB for a while (+- 15 years on and off, mediocre at best), but got the DB bug around May of last year. As I am a married with child type of person with other expensive hobbies, I wanted something to "get my feet wet" with, and didn't have a lot of cash to play with. I saw that exact same bass, from the exact same place on fleabay, and was very happy when a "lefty" came up on auction. But, I noticed in many of the sellers other listings that I could "flip the strings and bridge around and convert it to lefty". Now, I may be dumb, but I ain't stupid, and this raised a red flag to me, but not high enough on the pole to keep me from impulse buying a Crap and Mona (Cremona) from a mail order band/orchestra place.
I awaited the delivery of my prize with baited breath.
In the meantime, I learned minor things

about the instrument; details like what a soundpost and bassbar were, and how, (since I ordered a righty), how my new bass would never ever sound even close to right. I found out that the bridge was specifically cut for the factory (i.e. right handed) setup, although laughably so in hindsight, so I would a) need a new bridge and b) pay someone or learn how to myself cut one. More $$. I also found out that the strings were only really useful for holding the tailpiece in place during shipping. More $$.
I received the bass, and began the arduous task of setting it up. I really didn't comprehend the true meaning of "Ebonized" until I saw it in person; I think the closest comparision to what was on the fingerboard is the rust preventative undercoating that Ziebart used to sell for $99.99 in my neck of the woods. Buzzed as bad as you can imagine. Still, I tried to remain optimistic (i.e. delusional) about the whole affair.
Within three days, the endpin had failed, and needed to be replaced.
Quick order to All Hail! Bob, and I was back in business ($). As the "instrument" acclimated to the drier fall climate, the soundpost began making itself known as a prominent bump on the back. I learned how to trim and set a soundpost (sort of), and this process was aided by buying a handy dandy soundpost setter ($).
For whatever reason, I hadn't the faintest clue about Talkbass at this point, but stumbled on it during a Google search on "Cremona". needless to say, I was a bit crestfallen, as it seemed I had bought the worst of the worst, but at the same time, I was motivated, because I realized how much I really enjoyed the instrument, Ziebart buzzes be damned.
Around about November, I decided that I hated the Crappytona, and found out that a few manufacturers were doing correct left handed builds (Shen, Thompson, Engel, Upton). At this point, I had officially thown $781 (plus tools!) at an "instrument" that I had already outgrown. I bought it thinking the exact same thing you alluded to (I don't care about the tone, I just want to learn, etc. etc.), but within a month, I had lost any real interest in my EB's, and was ready for a new instrument, and also finally admitted to myself that a 41.5 inch board with four strings would have been a similar "learning" tool.
More $$$$. . .
Jump ahead to 3 weeks ago, and I just took delivery of my new, made for me (or another left handed mutant) bass, and it is WORLDS better than the money pit I bought to "learn on".
I tell this to help you out at the risk of humiliating myself a bit more on TB, but to save you from going through this nonsense.
Seriously, if I had not done this stupid thing, I could have afforded an Upton in another month or so, even though I am happy with what I did eventually get. I also had the opportunity to learn how to put a ton of lipstick on a very unattractive pig, for whatever that was worth. Certainly not $781.
I noticed that you have quite a great collection of EB's, and I really think you would end up at the same point I got to with my CCB, although probably quicker.
If you have waited 23 years before persuing the DB, what is another XX months/years to do it right? At the very least, play a few DB strung incorrectly

to see if you even like the damn thing. Rent one, even.
Cheaper than what I did.

Good Luck!
Brian