Know-How Exchange : Strategy

I am currently working with a client, who is very much interested in finding ways of measuring the very immediate (i.e 1-12 months) advocacy effect of the experience days they run for a luxury car brand. i know we can measure through repeat purchases, but cars generally get purchased evey 4-5yrs so thats no good. I am looking for innovative suggestions about how to carry out this measurement. A little background - the firm run experience days for a luxury car brand where customers are put up in a hotel( somewhere in the country side) and then driven in the luxury car (they already own) by driving specialists to show them how excellent the car handles, all the available technology in the car, how the car reacts with the technolgy on and off, etc..
I am looking for suggestions on ways of measuring the advocacy effect of these experience days run by my client.