I too have noticed that in my 2000 C230 it is a bit harder to maintain a straight line in a crosswind. I have the stock 205 55 16 Continentals on it and I think that they may be part of the problem. It acts like there is too little castor in the alignment. I have not had it above 95 MPH yet but at 80 it was very nervous and required much more attention than my 88 300E. With only 8K miles I don't believe that wear is a factor. I will probably put XGTs or MXV4s on it when the time comes, maybe that will help.
88 300E 225K Sold
2000 C230K Totaled @103K
2003 ML320 140K Granddaughters Limo
2009 E350 4Matic Sport 37K Sold
2011 ML350 44K