Aren't PNB's the equivalent of 'bling' though, in that pretty much their sole purpose is to say 'Look, I can afford to buy this useless item, so I will'.
I waste money on needless things all the time so I can't claim to be frugal or the arbiter of taste, but when I buy more expensive things I do it because they are qood quality, they look nice, or they suit/fit me better than the cheaper equivalent.
Isn't there are argument that none of that applies to number plates, which are just a way of brazenly demonstrating wealth - kind of the driving equivalent of having BURBERRY or other brand written in big letters on your clothes? 'LOOK WHAT I PAID FOR THIS' etc, which is tacky by any definition?
A car itself can be very expensive, but that money buys you performance, reliability etc. You are paying for quality, not just show.
I'm not saying people can't spend their money how they please, they can of course. I'm just saying why they may be seen as tacky.