I use gyft.com to spend my cryptocurrencies.  I convert my navcoins to bitcoins and then buy a "gYft" giftcard with the bitcoins.  With a gyft giftcard I can buy giftcards from dozens of retailers, including Amazon, Ebay, Macys and Walmart.  Sure, the process is not as fast as a debit card, but it works and, on occasions, I convert somewhere between $500-$1500 worth of navcoins to buy giftcards on gyft.com without a problem.