Different strokes for different folks. I think its decentralized nature is its least valuable aspect. If the only thing it accomplished were smoother and cheaper internet, small business, and interpersonal commerce, it would be incredibly valuable. The novelty of it (which I think has a lot to do with its decentralization) is currently causing too much volatility to make it useful for actually buying and selling things. A more boring government-backed (or -regulated) variant would be more useful and extremely valuable.
Decentralization is very expensive because it requires mining, so if you don't think that's important you should probably back a more efficient system like Ripple or Open-Transactions.
Expensive for whom, how exactly do you quantify that? Today we pay fee's to institutions which have massive infrastructure costs (along with their necessary profits). If anything, decentralization offers an incentive for the technically inclined to reap some potential rewards which is far more feasible than today's systems.
If you don't think decentralization is needed then Ripple is just as good as Bitcoin but it requires no mining. So the expense is the wordwide cost of all Bitcoin mining which is estimated at over $100M/year.
