Will the energy cost and deflationary nature of Bitcoins doom the currency to obscurity?
On the deflationary death-spiral part:

The bitcoin wiki has a good discussion of deflationary spiral, so that's a good place to get a counter point. 

I'd like to make some of my own (amateur) observations:


Gold is currently not the most popular money used in the world not because gold is "bad" money, but because:

a) Laws make it more difficult/expensive to use for day-to-day transactions then nationals currencies (e.g. legal tender laws require capital gains tax to be collected at the time of purchases in gold), and; 

b) Banks are incentivised to use fiat through the fractional reserve banking system. Why hold gold for customers when you can hold national currency and generate an order of magnitude more interest by loaning out 10x the deposit amount that is guaranteed by the central bank?

To put it another way, the absence of gold used today for your average transactions is not because citizens fear deflationary death-spirals, but because governments have purposefully made it less beneficial to use gold.
Bitcoin has been around long enough that we can at least get a sense whether falling prices has been a disaster. As far as I can tell that is not the case. All the major bitcoin  merchant services like BitPay, CoinJar and Coinbase record ever increasing purchases/sales made through the website. Yes, more people are using bitcoin, but one person spending money in the bitcoin economy is counter to the death-spiral theory. If the theory is correct, no-one should be spending bitcoins. 
The deflationary death-spiral, when you think about it, describes something that in layman terms sounds pretty awesome. Theoretically prices will keep dropping to $0, meaning at some point, everyone on earth will be able to buy everything and any service for 0. Sure, the theory states that e.g. everyone will lose their job, but who cares when everything is free! At that point you don't need a job.
When I've heard the (in)famous cases of deflationary death-spirals mentioned, they seem to always conveniently ignore the broader context. For instance, the Great Depression happened at a time when the government purposefully reduced the money supply, i.e. it wasn't like the money supply was stable or predictable (like gold/bitcoin). In other words, I'm yet to hear of an example of "bad" deflation that "just happened" during a normal period of dropping prices. There's always something else going on in the economy.