I'm sorry this post is quite wordy. Feel free to skip to the summary of my suggestion at the bottom. Please post if you would also like to see these features.
In the iTunes Miniplayer, you can select songs by an album, artist, genre or playlist.
When you select an album, you can choose a specific song from that album and play it. Thereafter, the rest of the album will play. Great. I love the behaviour of the Miniplayer in this case.
But what if I want to choose an item from a playlist and then listen to the rest of the playlist? Then I have to select a playlist and hit "Next Song"