It's not unusual for some players to play more than 30. Of course the better you do, the more difficult it is. Rainer Schuettler normally plays 30+, in his good year last year I think it was "only" 28.
Vilas playing 33 and winning 17 was incredible. I don't think anyone in the ATP could manage that kind of effort nowadays. Federer has won 10, but will have played less than 20 tournaments by the end of the year.