A lot depends on your taste in wood whether to stain or not. Forty years ago yellow pine was more common. When my dad remodeled the house all the trim he bought was yellow pine and we stained it. A lot of people then were still putting solid wood yellow pine paneling in their houses and it was stained. Today most people don't like the stripped look to yellow pine. You might sand some of it off and stain it with some different products and see if you like it or not. If you don't like it you could just paint over it. On the kitchen in my dad's house he put paneling in it that had almost a pickled look to it. We used a water based stain on the trim and it seem to subdue the grain better. Another option is a gel stain. Instead of penetrating like a oil stain most of the color lays on the surface.