@phaedrix: SmashTunes works great! ( That's an obvious remark, since I'm the author of it ;-) )
SmashTunes is named SmashTunes, because I created it before Spotify even existed. Its main purpose is to show the current playing track in the menu bar, but offers other options as well, like keyboard shortcuts, skipping tracks, etc. It offers some extra features with repect to iTunes, because iTunes is more "open" to 3rd party devs.
When you both use Spotify and iTunes, it automatically pauses Spotify when you start iTunes and vice versa.
It is not free. I ask a small fee to make up for the effort I put into it and to cover the App Store costs.
I was also frustrated by having to open Spotify to see what's playing, so I built an app. This app lets you control the player, and it also works with iTunes. Instead of showing the text in the menu bar itself, it shows it in a popover window when you click. Click the track artwork to open the main Spotify GUI. Download for free at https://mborgerson.com/trayplay/. It's also open-source, if you're into that sort of thing.