You wont fix this by adding to current mechanics imo. You would need a whole new mechanic that people are willed to spent their money on.
tldr: add some kind of housing/teambases that requires rent or other money sinks, ty (pretty common moneysink in other mmorpgs)
as soon as the option to buy the vanity for RP the RP Price doesnt matter anymore - its just about what you can get in pure pokeyen on the market at this point. It just gets crushed by the much greater supply