To answer the limited edition question about knowing which games can go for more after market, I believe it has to have a few requirements to be a safe investment.
If they can only be bought directly from the game company website that usually limits their production run. For example, the EA Dead Space Ultra Limited Edition of 1,000 (these cost $150 but sell over $400 when you can find one) and the Capcom Super Street Fighter Dojo Edition where it was said to be less than 1,000 (cost $80 and I sold mine for $240).
Also, if the game company is not a huge distributor that floods the market with their CE like Atlus, then their CE will go up like you seen with Demon's Souls.
I am a CE, LE, UE junkie and I admit that I have had more misses like Bio2, any UBI CE, GOW 3 UE, etc... and the common denominator for safe investments for me seems to be the above requirements.