I haven't done any really high-profile gigs, although I have played a wedding and some private parties (not the super-high-class ones, but paying events in decent venues indoors or outdoors). I've also done the standard bar and club gigs. I own two six-strings, but I only take one out all the time as the other isn't replaceable. I now own a four-string Ibanez, but it wouldn't serve as a backup for the six in the ways that I use it.
If I were to end up with more basses down the line, I probably would bring backups (Mono makes a great double bag, and I already own both the M80 Classic and the M80 Vertigo) to gigs just for the peace of mind, as I like to be prepared. I usually have strings, a battery, and spare cables in my gig bags, but I don't own a spare amp/cab or a spare Helix. (I probably should carry a spare strap, but I don't think that my leather ones will fail.) Of note, I don't drive at the moment, so my loadout has to be something I can carry all at once. It makes the logistics more difficult.