Of course, democratic presidential candidates stand for relevant things. Usually that is how each candidate is different from one another. Sometimes they stand for things that are controversial, like different stances on abortion. Sometimes the stances the candidates take are minimal and are not too different from one another. But they still stand for relevant things. That is how they get elected or not elected.
Naturally, if a US citizen is a part of the democratic party, they are going to gravitate more towards the democratic presidential candidate. So, yes, they can stand for something relevant; however, that, in my opinion, would pretty much be it. Other then that, they are just another presidential candidate.
Democratic party presidential candidates are the most patriotic and pro America candidates that we can ever have. They stand for relevant things like environmental rights, equal rights for all people of color and sexual orientation, and ensuring access to health care. What do the Republicans give us? Nothing, unless you're a corporation.
What a person decides to stand for will vary, but the Democratic party in general usually stands for helping the poor, minorities and disabled, helping the elderly, lgbt rights, women's rights, the environment, the arts, and space exploration. The Democrats are also generally not so wasteful on national defense and military spending.
Some democratic presidential candidate stand for relevant matters and try to make a difference for the country, just like some republican candidates stand for matters that are good for our country as well. It comes down to each candidate them self not all the candidates as whole from one political party.