The reason why Lula's 80% approval rating is not translating into a Dilma lead is because there are little differences between Serra and Rousseff on how they are going to govern Brazil. The main difference is experience and that is counting heavily now in the polling responses. The Brazilian people already know Serra who was the Governor of the state of São Paulo until recently and he was once the mayor of the city of São Paulo as well. Serra won and lost elections and he was a pretty successful health secretary for Brazil fighting a drug corporation in breaking patents to help HIV patients in poverty. Rousseff, on the other hand, never even ran for office and she was hand picked by Lula as his heir.
There is no easy way to draw the line to find which party is true left and which is true right. PSDB (Serra's party) is mostly liberal and based on the American Democratic party. PT (Lula's party) is a left wing party as well but its alliances tilt it a bit. Lula's vice-president, for example, is a conservative and Dilma's vp is likely to be a PMDB conservative. A lot of prominent left wing politicians left PT and joined other parties (including PSDB) since Lula became president.
There are some interesting developments today in the Brazilian media with Ciro Gomes (presidential candidate for the Brazilian Socialist Party) really upset with the behind the scenes work to take him out of the picture. Ciro Gomes is accusing PT and Lula of making threats to drive him to quit. The Brazilian Socialist Party is supposedly going to announce that Ciro Gomes is officially out of the race this coming Tuesday (I'm sure news will come out in the American media in the next few days).
Ciro Gomes is pissed (source in Portuguese about his interview tonight on SBT which is a major TV network:
http://oglobo.globo.com/pais/mat/2010/04/23/ciro-gomes-critica-lula-diz-que-serra-mais-preparado-do-que-dilma-governo-minimiza-as-declaracoes-916418662.asp) and PT is now trying to woo him for damage control because his followers in the state of Ceará are going to be pissed and they might vote for Serra. That's a possibility given the dynamics in Brazilian politics. Winning the northeastern states by large margins are crucial for the PT candidate.
Marina Silva is also very upset that Ciro Gomes is going to be out of the race. She is criticizing those who are forcing him out and she is saying that the lack of options is hurting Brazilian Democracy. (Source in Portuguese with Marina Silva explaining why Ciro Gomes likely exit will be a step backward for Brazilian democracy:
http://oglobo.globo.com/pais/mat/2010/04/23/marina-diz-que-saida-de-ciro-da-disputa-retrocesso-916422760.asp)