Yes, in Spain and in other countries in which democracy is valued, protests from citizens can lead to chage in political viewpoints and practices. Since leaders must listen to the voices of their constituents in order to be re-elected, they are much mroe likely to consider that which they consider to be the opinion or value of a large part of the population.
Citizen protests in Spain will only work if public services are shut down for a time and the country is brought to a standstill. Protests can work if enough people are affected by them. Railroads, government services, hospitals and other services would have to be shut down before the masses take notice. But they can work to bring about changes, yes.
I believe massive citizen protests in Spain could bring legislative and political changes. I believe this is the case with any country that is willing to listen to it's people, especially when they can assemble and speak their mind. I think this can work for Spain without getting out of control.
I think that mass demonstrations will capture the Government focus on the citizens demands most of the time the Government will not change it's ways just because of a protest, the only way anything actually gets done is if there is a change in the Government and those who are protesting get seats in power.
I think as long as they are still mentally capable of doing the job, it should be ok. They still face checks and balances, through the other judges,but if they go insane, maybe that will be grounds for a judgement on this. It's worked fine so far,but everything can change with one event.