I had a play with MTGOX the other day. Managed to sell 9BTC for $17 each. Didnt relise how much there commision is so only ended up getting $16.8 for the each which pee'ed me off a bit so I made a buy order for 9BTC for 16.4 each which acutrally bought them all back so iv got all my coins back and 3 dollars in my account. Going to just hold on to my BTC now untill the mining difficultly goes right up at which point the price should go up too.
Just make sure you don't fall into the trap of correlation and causality. Price and difficulty tend to follow each other (within certain boundaries) but difficulty does not necessarily imply price. More likely it's the other way 'round - the more you can make per BTC by mining, the fewer BTC you have to make for it to be profitable. So far prices have only gone up over any reasonable span of time and difficulty has followed suit. At some point it will occur that price no longer justifies difficulty and rather than price moving up to accommodate as you seem to predict, people will stop mining and difficulty will move down.
Price increases because of the market, difficulty increases to follow price, so long as mining remains profitable. I made the mistake of confusing the two at the beginning myself, it's far too easy a mistake to make.