If I was willing a few days ago to buy at $100, then I can only see this as a good thing. I'm getting the bitcoins that I buy at a MUCH cheaper cost than I was already willing to pay. How valuable they are to me is not dependent upon how valuable they are to the people who are buying and selling at MtGox (or any other exchange). I know how much I'm willing to pay for them. Anything less is a great discount. Anything more and its time to stop buying and just hold on to them or spend them where possible. I adjust my opinion about value based on their security, and utility.
It may very well work out for you, but be careful. This was the same philosophy that bankrupted many people when they were buying the high flying internet stocks and kept accumulating all the way down in 2000.
Sure. That's why nobody should ever invest any money that would be devastating to lose in any risky venture. If you don't recognize bitcoin as carrying a significant risk, then you shouldn't go near it until you've done enough research to understand what the risks are.