This post is old, but I got redirected here and read many comments.
Many arguments about why the algoritm shoulndt do nothing outside the system have a workarround.
Some say that the solution having an extrincic value could desestabilize the system because of usefull solutions having intrinsic value.
I mean houmans are specialized in tasks and grouped by their specialization, one group knows little about the other and then cross platform solutions scarse.
For a start, there's gold and it have uses so it also has intrinsic value, there's gold on our computers, our teeth and lots of stuff meant to be durable, it's not usefull as a car or a kilogram of potatoes though.
An equivalent of gold in calculations would be any problem that hasn't any direct application and possible will never have but it's still usefull for knowledge just to satisfy curiosity, there's lots of unapplied math problems of this kind I think and they're worthless because nobody would care about it, yet is a problem intresting for humans that got a solution.
Other thing to add is that computer power incresed since this post and bitcoin somehow operated to maintain value by adding difficulty, hence as far as I know (not very much), mantaining transactions is an easy problem now so an additional task of solving the hawkings radiation would be an added difficulty that I assure you has a f*** of economic value.
I can question myself is the real problem is economist knowing few of unpractical solutions outside they're self made system, and that there is a miracle that some hackers involved to create the bitcoin.