I would say that if you're sharing the "cost" of the trip, it would be appropriate for the buddy to pay one-half of what would have been paid (the cost avoided). In this case, the cost avoided would have been the $100 - $150 per night for 10 nights you and your buddy would have paid had you not stumped up your points.

Alternatively, if you don't want to make "money" on redeeming the award, I'd suggest the buddy agree to contribute something to the trip of a value equivalent to the $1000 to $1500 in cost avoidance you contributed (and that would be much more than a nice dinner) -- perhaps the transportation for the trip and maybe meals.

Alternatively, he could agree to pick up the lodging next year.

Saying that the hotel didn't "cost" you anything (or nothing except for the out-of-pocket convenience fee) is false economics. Not only are you "paying" the lost opportunity cost (you could have used a "cash-back" card), treating the award as "free" ignores the effort (and possibly sacrifice) in collecting the 56K Starpoints.

My opinion, FWIW.