At this point I think that it’s better to roll for the random than to go for the specific.
That being said I think that the intent of the vendor was to essentially be the ‘bad luck protection’ system. If rng goes long enough without favoring you with the proper traits then there is a way to insure that you can get them however it’s just that, a last resort. The high cost seems to reflect the appropriate amount of time that they believe to be long enough to say that it’s taken too long to get the drop.
I would guess that the vendor was meant to correct bad rng as it’s primary purpose.