The bottom line, unfortunately is that almost the whole pet industry revolves around money.
In your case, if you think you might be willing to give it a try, my (probably highly disagreed with) opinion is to go ahead and give it a try.
While what you have is not ideal by any means, it's a step up from where the fish now is and will give you the opportunity to experience a "species" tank, where you have one large fish that has a chance to prove to you that they can indeed be very real, and often affectionate pets.
Later, if the Mrs. (often the final say in a BIG tank situation) gets attached, you have the door wide open for a LOT more enjoyment.
As deplorable as the shark situation isi regards to catsharks and bamboos, I feel it's much more deplorable when the fish offered for sale are baby Nurse sharks or Wobegongs, which literally grow into giants, and even worse, the number of green moreys that are now appearing, an animal that can truly be dangerous in the not too distant future.
Keep in mind that I have a stonefish in one of my tanks, acquired when a dealer friend ordered me a generic scorpionfish.....animals like this, in my opinion, should definitely be left to people highly experienced with venomous animals and absolutely be prohibited without special training/liscensing.
OH!......the nitrate problem can be assisted by growing macroalgaes in the tank corners and/or in the sump and by doing many more water changes than would normally be required.
