I certainly wouldn't take 2 pairs of SPD shoes on a trip. If one fails or wears out, it still should be able to push down on the pedals until they could be repaired or replaced. At most bring an extra cleat nut, and a few screws (I can't imagine an SPD cleat failing). I do like my neoprene shoes, and might choose them if expecting a lot of rain.

Most of my longer rides were pre-SPD shoes. And those old leather soled heelless shoes were uncomfortable to walk in and dangerous for marble stairs.

But, it would all depend on the ride. And that is what you need to decide. If it is mostly on the bike, I'd probably just take the SPD shoes and make do for those times off the bike. I find myself often riding dawn to dusk and sleeping most of the rest of the time.

On the other hand, if the trip involves significant time off of the bike. Say ride for a day, then tour for a few days, then ride a bit more, followed by more touring. Museums? Then I might consider some off-bike shoes. Still, if the touring part involved riding from museum to museum in a city or something, I might just do the SPDs (I don't ride flats, and the SPDs are uncomfortable without cycling shoes).