I always do carry spares but let's face it, a spare is useful in any critical situation. You've got to get it onto the bass and get it tuned and keep it at pitch. Even if the string has been played in, that's not going to happen.
I currently have Anima G, A and extended C and Garbo D. I was actually wondering if I should try the Anima D again. It's interesting that you think the Pizzicato could even be louder than the Anima.
I have some old Superflexibles in my bass bag for emergencies.
It's true that you'd have to stop to put on a new string if one broke on a gig, but something like a old Superflex would probably hold it's pitch fairly quickly. Using steel on the A&E isn't too bad unamplified, but I really hear the difference with a pickup. Of course, I use an Underwood and steel can sound pretty metallic with that.
I don't know if the Pizzicato E is really any louder. I'm surprised how bright and growly it is though. I like the Anima D too. The whole Anima set is good. A little more "sing" on the top end than I want in certain situations, but I like them very much.
Having said that, I played at the IBMA bluegrass convention a few weeks ago and plenty of those guys use Spirocores and get great sounds. I guess it all depends on the player, the bass, etc. I'm not really a bluegrasser, but living in Nashville I wind up doing some of that, and also Ray Charles-type blues and Elvis/Patsy retro stuff. Gut-like strings work very well for all of those kinds of music.
A few observations:
I always think players like Paul Chambers and Oscar Pettiford had pretty ideal sounds. Obviously they were gut players, but there's still plenty of liveliness to their sound. Now I'll assume that they had good instruments and those coveted gut strings of yore (and major talent!) People like me with cheaper instruments often find that sound somewhat ellusive when we use guts. It tends to sound a lot less responsive than PC on "Kind Of Blue"

But we are very lucky to have so many new string options these days. Between Eudoxas,Olives Obligatos, Evah Pirazzis, Pirastro Pizzicatos, Velvet Anima and Garbo, Gamut and Dlugolecki --you can blend strings that have varying degrees of gut and steel qualities until you find what works best for your particular bass. All it takes is $$
Sorry if I'm "blogging" too much here.