I'm not going to be able to change plans to meet a friend who was willing to drive 100's of miles to see me
Why would you not change plans? What will they think of you if you did that?
That I never value my friends enough
You should value your friend more. They are traveling a long distance to see you. You should change your plans to make room for them in your life.
I don't want to make my friend feel that their effort is not appreciated.
Then cancel your other plans, you already know it is wrong. You have to just go with it now and do the right thing for your friend's and your relationship's sake.