Agreed. Keen famously lost a bet on Sydney property prices many years ago so not many people take him too seriously.
http://www.smh.com.au/business/keen-to-climb-kosciuszko-after-losing-bet-20100216-o978.html
I do agree to some extent that you would be mad for spending bitcoin in its appreciation phase, but it depends on what you are buying. Would I buy a coffee in bitcoin today? No.
Would I buy a Rolex watch off overstock.com that I know will appreciate in value? Probably. Same goes with property (if I had enough in bitcoin) and other assets that have the potential for appreciation.
I spent a little bitcoin to purchase Steem, expecting Steem to double in price before bitcoin did. Steem then gained about 10%, while bitcoin is the one that has almost doubled. But I have no regrets... almost. :-)