I do actually have Quadruple Mysterious cats, as well as Quadruple Curious that I personally found more desirable despite not being the coveted 9 traits. I'll birth some after work and post pictitures.
Personally for me 9T is not the best cat, some eyes look better with Curious or Big as one or both traits and I love Natural Shade and often breed for it. Prior to Monochrome Whisker colour being released I would often breed for Silver to make a cat couture. I have always found that other breeders of couture cats apreciate this and it doesn't detract from value at auction.
I love to breed the dominant and think that can actually be harder as those hids love to pop and once they do you have lost your dominant trait, hanging onto a dominant trait can be tricky, pulling it pure is a lot more work, first you have to hide it in both genders, then check its actually hidden before attempting to pull it out from both cats to create a pure one, thats a long process of trial and error. That said there are breeders that breed for the recessive and thats ok too, we all have what we love and I think a good cat is one that you love regardless of value, a great cat is one you put up at auction and then wish you hadn't or one you can't bear to even think about putting up. I confess to many a sigh of relief at a no sale on my cats. Truly a labour of love here