They don't need to be commemorative plates either, a plate collector can collect such things as Japanese "Shiki" laquered plates or fine china porcelain. Some people relegate plate collecting as kind of a joke activity, saying that we only collect such things as Elvis or Dale Earnhardt commemoratives but that is simply not the case. Fine porcelain china though it is not a "commemorative plate" can still generate some very good value.
Whichever plates you decide to collect, be sure to give them the best care possible. Why go through the effort of making a collection without keeping them in tip top shape?