I have seriously mined LTC, VTC, DGC and DMD and I have dabbled in a few other coins.  I have heard the same arguments with all of these coins.  As the price goes down some supporters advise loading up at low prices while the skeptics ask what is going to happen to make their coins more valuable. 

This seems to be a fairly constant pattern.  When I first started mining LTC, about 25 LTC equaled 1 BTC. Today, its 97 LTC to one BTC and BTC is about 60% of the price it was then.  The same is true for the other coins.  The more I mined, the less the coins were worth and the supporters of the coins insisted the value would go back up.  The skeptics, including myself kept asking why?  With difficulties increasing and prices decreasing those who mine are falling further behind.  I believe ASICs have actually hurt the crypto markets because they have driven out large numbers o interested miners wo did not want to make huge investments in the technology but wanted to support the notion of an alternative currency.  I think this is one reason why VTC has done better than other coins even though its value has dropped significantly too.

I continue to mine DMD because of the efficiency of the algorithm.  It takes less energy to mine DMD so I get the most hashing power for the same electricity.  DMD mining software has improved too.  My ash rate is more than double what it was when I first started mining and I haven't added any new hardware.  Yet me energy requirements have only increase a few percent.  But at the current price of DMD, even with the efficiency and optimization, my mining is not cost effective.  The break even point gets farther away as the difficulty increases. I continue to mine because I still hold out hope the this coin will survive the inevitable flush out of most of the coins that are mined today.

The only thing that will drive up the price of DMD is interest.  People need to want DMD for some reason and it has to be more than just those of us who mine this thing.  Mining and investment alone are not going to work in the long run.  It has to be backed by commerce and demand.