Simple point the mechanic is making is leave your car sstandard on standard rims and tyres or you will ruin it........but where is the fun in that
On the flip side as awesome as my gtiii was handling wise On run flats and trd shocks and springs, the comfort level was so bad even On motorways that I had to get another car for commuting
As for the argument that pollys make stuff wear out faster. I don't really buy that as the stuff that wears out on Celica suspension is the oem rubber bushes and Toyota will only sell you a new arm, factor in that if one side goes you should really buy the other and your into hundreds of poundage for rubber crap that will wear our again in a few years