Could bitcoins be used to filter spam? I would like filter spam in a way that people have to pay a very small amount of bitcoins to prioritize very good things or to kill very poor things, to make less casual environment and to encourage good filtering. Later best filterers could be rewarded with bitcoins. Is this possible or does this bloat the chain?
Using Bitcoins as a reward and micropayment system is possible. You wouldn't want to send a separate transaction for each micropayment (fee/transaction ratio would be quite big), but you can pay everyone down to a couple decimal places for each operation they make say, once a day.  Details of implementation would vary, depending on what you want to do exactly.