What style/duration of tour? For a 2 week tour they should be fine but a year-long continental tour would be pushing your luck regarding spares.
Assume that you wont be able to get touring tyres anywhere (pretty much the situation with 700c in many parts of the world)
Take at least one spare 28mm tyre and have backup spares ready to be sent out to you.
If you are considering a bike for purchase, use 26" MTB wheels rather than 650c.