If you're having trouble with Mustard gas getting him to do his thing... might want to sell him or try show him a female for encouragement, remove tank lid and see if he blows bubbles in cold air? if you think he's genuinely old that's how you will find out if he wants to breed or not.
The whole VT thing... I sold one for $15 a while back depends how well you advertise and the quality of your photo.
IMO There is no supreme tail type in this type of fish... they are all same species and yet some clubs frown upon crossbreeding. Whatever is the most (aesthetically pleasing) popular is what breeders aim for hence the high amount of attention paid to "DUMBO" and HALFMOON
The market ran out of spadetails that way, they are real pretty but some call them an eyesore.
There are exceptions though with any fish like Dragon VT with good scaling... some breeders may be interested but currently its just a fancy thing with people saying things like "I have a special fighting fish" "crowntail is better than halfmoon blah blah blah"
I'd use a good VT for coloration or to start a new line but once I went plakat I knew I would not find anything more stable yet plakats are cheap as chips lol.