Disclosure: I am long on both bitcoin and freicoin.
You got me! I am, in fact, the co-author of Freicoin, and obviously very bullish, although my estimate of its future value has non-trivial discounts due to outstanding risks. In the economic model of Freicoin, the two currencies perform different, non-competing functions (store-of-value vs medium-of-exchange) and are perfectly capable of co-existing. Indeed, one can argue from inside the Freicoin perspective that both currencies are inevitable.
There is no proof that no other mutually compatible coin is possible, but nor is there any example other than Freicoin. Altcoins generally fall into three categories: those which are param tweaks of bitcoin (e.g. Litecoin), those which add features (e.g. Darkcoin), and those whose differing monetary policies from bitcoin make them stand apart as generally useful and compatible. The first two categories are useless as anything which tweaks params or adds features could be done in bitcoin directly or in a side chain, and Freicoin stands alone as the only example of the third case.
I try to say this from as unbiased a perspective as possible, but of course accusations of bias are incredibly easy to make here. I co-created Freicoin and still hold a large but decaying number of freicoins. However I spent as much time as I did on Freicoin because I believe the above.
Every other alt out there is junk -- including the ones you mention -- although I won't rule out the possibility of a another coin which differentiates from bitcoin and freicoin in a compatible manor. Although honestly I don't know what that would look like.
That's a very nuanced view though. So honestly it's just easier and less likely to be misunderstood to simply say "all alts are junk", and leave off the special case of Freicoin unless I have time to explain in sufficient detail.
In early 2000, I registered my personal domain name weidai.com, along with a couple others, because I was worried that the small (sole-proprietor) ISP I was using would go out of business one day and break all the links on the web to the articles and software that I had published on my "home page" under its domain. Several years ago I started getting offers, asking me to sell the domain, and now they're coming in almost every day. A couple of days ago I saw the first six figure offer ($100,000).
In early 2009, someone named Satoshi Nakamoto emailed me personally with an announcement that he had published version 0.1 of Bitcoin. I didn't pay much attention at the time (I was more interested in Less Wrong than Cypherpunks at that point), but then in early 2011 I saw a LW article about Bitcoin, which prompted me to start mining it. I wrote at the time, "thanks to the discussion you started, I bought a Radeon 5870 and started mining myself, since it looks likely that I can at least break even on the cost of the card." That approximately $200 investment (plus maybe another $100 in electricity) is also worth around six figures today.
Clearly, technological advances can sometimes create gold rush-like situations (i.e., first-come-first-serve opportunities to make truly extraordinary returns with minimal effort or qualifications). And it's possible to stumble into them without even trying. Which makes me think, maybe we should be trying? I mean, if only I had been looking for possible gold rushes, I could have registered a hundred domain names optimized for potential future value, rather than the few that I happened to personally need. Or I could have started mining Bitcoins a couple of years earlier and be a thousand times richer.
I wish I was already an experienced gold rush spotter, so I could explain how best to do it, but as indicated above, I participated in the ones that I did more or less by luck. Perhaps the first step is just to keep one's eyes open, and to keep in mind that tech-related gold rushes do happen from time to time and they are not impossibly difficult to find. What other ideas do people have? Are there other past examples of tech gold rushes besides the two that I mentioned? What might be some promising fields to look for them in the future?