I have been to Universal the past three MLK weekends and if the weather is nice, it will be a bit crowded.
Three years ago, it was flat out cold in Orlando. I am talking about the temp never hit 50 all day and got into the teens at night. We walked onto everything that weekend.
Two years ago it rained but was warmer. We walked on to most attractions. At most, we waited 10 minutes for Earthquake to reset and load in.
Last Year it was nice. I was sporting shorts and it was crowded! We stayed at the Hard Rock so we didn't have to wait, but I think the average coaster wait was around 20 minutes with Spider Man running 30 minutes.
And to answer your question, staying on property means you will skip the lines! It's a great treat! It also works at City Walk restaurants as well! Show them your room key and the wait to be seated won't be as long!