Spiritual is far and away my favourite trait. It allows so much versatility and so much efficiency within an empire that it's unbelievable - IF you use it. I agree it's pointless if you just play a normal game and save yourself a few turns of anarchy.
One thing that took me a little while to get is that, as the name implies, it really does go hand-in-hand with strong religious focus. The first aspect is the religious civics, which is the column Spiritual can abuse the most anyway.
You can always easliy switch back into slavery/OR and whip out a horde of missionaries to easily spread any religion of choice throughout your civ - letting you get the most from the civics. Theocracy can let you generate a well-trained army right across your civ. Bursts of CS/Pacifism are INCREDIBLE for generating GPPs across an empire with little pain, and are one of the major reasons why Spiritual rocks.
Once you get Free Religion, most people will sit there with it constantly on. With Spiritual, you can go for jaunts back into the other religious civics and get the benefits of other later civics in other columns. Universal Sufferage/OR gives a nice discount on rushing buildings; Theocracy is still great for late-game wars; Representation/Caste System/Mercantilism/Pacifism will generate huge GPPs in short order while still giving nice research. I often like to go for short bursts in the religious civics and set research to zero, then go back to FR and get the 10% research bonus on 100% of my commerce.
Mid-to-late-game happiness is also a massive bonus of Spiritual. With easy OR switching, you can build heaps of missionaries for every religion in your empire and spread them to all your cities for a great happiness boost when you go to FR, and building cheap temples for each religion can be a very worthwhile use of hammers for happiness post-HR.
In the other columns, switching briefly to Universal Sufferage and/or slavery + OR can be very good for quick rushing of buildings; quick bursts of Nationhood to draft up a nice army in a hurry (and you've got extra happiness to compensate too); Vassalage for units when you're not running Theocracy; Serfdom when you get a new worker tech (Civil Service, Replaceable Parts, Railroad etc) and need improvements in a hurry; Free Market for commerce and corps, and State Property for war and production. Environmentalism when you've been hit by poison or you want to heavily industrialise.
It isn't at all rare for me to switch into every civic multiple times in a single game.
There's also the diplomatic aspect. You can always switch religion (or switch in and out of no religion) for diplomatic purposes, and again it's easier to quickly duck into OR to quickly spread a new religion if you find you've backed the wrong horse. Quick bursts in a different religion can be great for new trade opportunities, or just for lots of lovely backstabbing.
EDIT: I forgot to mention that Spiritual opens up opportunities for a whole different type of hybridised economy, not just with civwide bursts of CS/Pacifism in a primarily cottage economy, but also a Liberalism/Nationalism/Constitution beeline and a major jaunt into Rep/CS/(Mercantilism)/Pacifism and scientist bulb a lightning-fast path up to biology/medicine, a switch to slavery once the food bonus kicks in and whip buildings, found sushi, then go democracy and build up those cottages with emancipation.
Some people say it's worthless now that Golden Ages have changed, but for that to seriously contend with Spiritual you'd have to be criminally underutilising Spiritual in the first place. Plus you can just spend those GPs on stuff other than Golden Ages anway! Christo Redentor is too late to really contend. Plus the Shwedagon Paya is a fantastic wonder for a Spiritual civ, and can easily make up for the Golden Age thing. Also, with the extra spy buildings, switching US/slavery/OR for the buildings and back to Rep can give very nice benefits for very powerful late-game specialists.
I love Spiritual so much!