What is reasonable mileage is so variable based on rider, weight of load, terrain, wind, and other factors that it isn't reasonable to really expect one person's or one tour's number to be even close to another. I think that it can be fun to do long mileage and also to do easy days. I generally do some of both an any tour, but do like to knock out longish mileage.
One thing I find is that on longer tours it makes sense to take it easy the first week or so and then build mileage as you go. If knocking out a lot of big miles is a goal I still think that starting out easy is way better than doing hard days at first and then needing rest days just to survive. I know this is not the norm, but I personally prefer to not take full rest days unless it is for some special place that I want to spend time doing something interesting. I do sometimes take easy days or half days.
If I had to be pinned down to pick a number, I'd say the most folks probably fall somewhere in the 50-80 mile per day range on long tours. We did the TA averaging 60 miles per day with a fairly heavy load and I tend to do more like 80 miles per day now that I pack much lighter. To calibrate that I will say that I am 64 years old, reasonably fit, but not a natural athlete, and don't ride all that much when not on tour ( I do trail run to maintain general fitness).
For me having an open ended schedule and no planned daily stops is the way to go. That way I can ride as much or as little as I want on any given day.