Spark Plugs are not going to make any significant gains in HP, however a change in air filter may net you 1-2 extra HP. Most after market drop in type filters will flow air better than the stock filter. I recommend the Pipercross Air Filter.
Since the FI version bikes you have in Brazil run on 100% ethanol you will need more than spark plugs and an air filter for any significant gain. New full exhaust, power commander, O2 sensor removal plug, air box removal and ignition/timing changesare other options that will help in gaining HP. You could possibly see a 3-5 HP gain over the stock 32 HP.