My experience with Burstcoin mining is that while it is indeed far more efficient than coins that are mined with GPUs, it gets similar efficiency to the coins mined with cheap smartphones but the initial cost per profit is much higher. Therefore, I just mined it with a HDD that I got on sale, making back about half the cost of that HDD before I used the space for other purposes.
Pretty much everyone has spare HDD capacity lying around and some intelligent software to use that for mining but immediately return it to the user when needed would be a good way to make use of it.
What I would like to see is a cryptocurrency mined by hosting content with low cost, low power computers like Raspberry Pi, with the goal of making an alternative to Youtube. Going a step further, a cryptocurrency that's mined by creating a P2P wireless mesh network would be even better although I don't have a clue how such a system could be made to work. (Maybe in the beginning, users could effectively get paid to share their Internet service with something like Tor, I2P, or VPN to avoid the usual problems with doing so, while other users could pay to access those wireless networks.)