So I was thinking about trading my scalding tarn and Marsh flat for a Liliana of Veil. I just want to collect all of the liliana planeswalker versions out there. A friend who have played this game a lot longer than I have told me to hang on to the lands because the price will go up in the long run. I google scaling tarn price history and I don't seeing it top out over $60-70 range unless it is those foil masterpiece. Just need some advice from players in the game. Should I hang on to them or trade them?

My advice is not to speculate on the price of cards and do what gets you closer to whatever goal you have set for yourself. If your goal is collecting Lilianas, those lands aren't doing anything for you.