I'm going to do a ten-day long tour down the west coast of New Zealand. I'll have some luggage in rear panniers, but no tent (staying with friends and in backpackers accommodation). There'll be a fair bit of uphill and downhill on some days. But I don't forsee that I'll hit gravel - I'll likely stay on sealed roads. Of course, it may rain (as if that isn't obvious).
My bike is a steel framed road bike, and I currently ride with 23mm tyres. Because it's an older bike I can fit wider tyres on, which some recommend for touring, but I wonder if it's worth it? In the context of my tour, if I went to 28mm tyres what would the advantages/disadvantages be?