Haven't bought any .asia. This has similarities to the .mobi debate, except I'm pro-.mobi and anti- .asia as far as investing in the extension goes.
The top keywords will have demand in .asia, like casino, sex, money, business, but beyond that I don't see much potential just from a domaining standpoint - if you build a website on your .asia and promote it then sure you can do well with .asia
Most of the people in that region don't even speak english (look at the country list), so how well can english domains do on an extension with four english letters? The people in asia won't use them to market to each other, and people in english countries would rather use .com .net or their own country code.
I think the better way to play the region is with IDN .com domains, or country code domains like .cn and .in and .jp
Look at what happened with .eu, the odd sale of a good keyword or keywords is all you see.
Protecting your brand or buying a number of favorite keywords/terms within affordability is reasonable, but I wouldn't break the bank or go 'all-in' with .asia.
Good luck to everyone who own .asia, hopefully my hunch is wrong.