2 engines with the same problem? wow, you must be the most unluky guy out there. what are the odds? but this can happen with any car manufacturers, not just Nissan. If the problem was as large out there as you think, Nissan would issue a recall, but all I read are good reviews and happy owners, except for here. As for law suit, if they are replacing the engine, I don't see what else is to do. I don't thing it will diminish the value of the car either. It will be done by the company and it will be a brand new engine. I don't see how this can affect the value of the car. Heck, nobody will even notice if you ever sell the car.
Also you have no certitude if that problem was not in the previous years of the Micra since you obviously cannot know if every cars sold did not endup having an engine replacement. It's probably isolated cases. Before I came to this forum I only heard good things about that car from those who owned the Micra. Probably those with a problem are looking for such place as forums to search for similar problems and so we see most of the problems endup and have the false impression that it's a bigger problem? not sure.
I am really sorry for those who have this problem. So far my car has 1200 km and no problem but I will keep an ears for it for sure!