Well if you speak of price you probably mean something like the actual price at mtgox. Now if you wanted to change the displayed price at mtgox you would have to sell for let's say 50% of the usual price to your own account. But at mtgox or any other exchange you don't trade with a specific account. You always go through the orderbook. So to buy or sell to your own account at the manipulated price you would first have to complete all orders inbetween. At that point it does not realy matter if you buy your own stuff because you actualy did change the price for real.
So that's probably not price manipulation in the sense that OP had in mind. Like you said, that's through the order book and no coins are actually moving to different wallets.
You can do that but that won't change the price of a Bitcoin whatsoever.
Not sure what you're referring to. If you're referring to DerKorb's comment, then yes, the price has in fact been changed. I wouldn't call that manipulation though and it sounds like a good way to just lose bitcoins in trading fees.
OP, with regards to the idea of selling coins to yourself using localbitcoins to manipulate the price won't work as you said. I'd say the volume is far too low to be of any significance. I suppose you could make a trade on localbitcoins for 10x the current value and hope to get media attention though.
As for CoinDD, like Crazy_rabbit said, you would need huge amounts of bitcoin to create further hype and hence move the market. This could only potentially work with some of the smaller altcoins.