It has become very apparent from this thread that the people fall in to one of two groups.
1) Those why like / appreciate private plates
2) Those that don't.
I can't see the problem here. Think of them as an accessory, one that you can take from car to car (providing it's not car specific that is). Some people like 20" alloys, some don't. I personally think that if it make you happy then what's the problem?
The right private plate is far from being a waste of money. I bought mine for £250 from DVLA many years ago. I have had more than one offer well in excess of £2.5k. I consider it a good plate and people know me and my car because of it.
Personally, I'd not go for the S3 XYZ type plates because you are unlikely to have an S3 forever and for most, the three letter initials type plate will only be obvious to the owner, but does it really matter. People buy different things for different reasons.
So, if you find a plate you like and it's within your budget, then buy it! or if you'd rather spend the money on a holiday... send us a post card.