Simple idea. Players just don't get any numeric stats about their character. At most they would have some sort of generic statement along the lines of 'You look Very Strong.' Players can get a general estimate of how they measure up to other characters via various competitions, duels and other such in-game feats. No numberical stat values displayed in-game at all. No, 'You gain 1 Agility' or 'Your skill in Basketweaving increases by 0.1' or any such overt, spreadsheet-encouraging nonsense.
Your character is defined by their actions, not by an in-game spreadsheet. If the players find some way to reverse-engineer their stats, that's fine, but the game won't support them in such endeavours, nor will it cater to the number-crunching crowd.
[Cross-posted this on the MMO Roundtable forum here]