1. What gives Bitcoin / Goldcoin its value ?
Cryptocurrency values are primarily a function of supply and demand. The more useful the currency, the more desired the currency, the greater the number of adopters, etc. - the greater the demand (aka network effect). The supply on the other hand is a product of the coin generation rules. Goldcoin has a fixed number of coins to be generated at a declining rate, a rate which decreases annually.
The markets work as a price discovery mechanism. Currently, there are but a handful of merchants accepting Goldcoin, there are probably only 25 active, real, community adopters/speculators, and the Goldcoin currency is entirely unknown to the outside World. These attributes have resulted in a price discovery of $0.01 per coin.
Since we know that inflation rate is declining, if the adoption rate remains constant, the price will increase moderately over time. However, if the adoption rate increases (demand), as inflation declines (supply), the price will rise dramatically.
2. Why is it assumed that Goldcoin will follow the same pattern as Bitcoin, ie: why do we talk of a 1 dollar and 100 dollar range per coin ?
I'm not sure this is assumed, but if we can gain some traction and grow the community, continue to evolve technically, gain the interest of outside developers to contribute to the project, and work hard to promote the coin, I think we can compete with Bitcoin.
Since Bitcoin is currently priced at $400 and has a similar history and underlying characteristics, then it is reasonable to think Goldcoin has the potential to reach $100 per coin if we continue to execute, organize, and grow.
Goldcoin has a much more brandable name than any other crypto, a name that tests well with consumers, and we have a superior developer. If Bitcoin becomes commonplace in the mainstream, consumers will look for options, and Goldcoin would become a sensible, viable, and attractive option.
3. Will the new Wallet come out supporting any other coins, or only Goldcoin at the start and plugins will have to be written for the others ?
It is my understanding that the new client will be 100% open source, allowing software authors to write plugins for various other coins and applications. I think at the start, it will support Goldcoin only. But we'll need to confirm this with Akumaburn.
4. Why doesnt Goldcoin approach online gaming eg: Dota 2 as a payment option for in game purchases ?
This is an excellent idea and one the community should consider pursuing.