I was stopped in Minnesota for being in an old van with out of state plates. It was towards the end of the Sturgis bike rally and I was driving away from it, purely by coincidence, so he assumed I was there selling drugs. He asked if I had ever done any drugs in the van because the K9 unit would smell them. I just chuckled and said there was nothing to smell, I don't even drink. He let me go. I had a similar stop in Nevada but I had Nevada plates and a new van.
Out of state plates will draw a small amount of extra attention especially if you're in the same place for a while, but I don't think it makes a huge difference most of the time.
The best choice for where you get your plates has been covered in other threads.