Nigel, we see and hear of bikes with very high millage but don't always see the cost of those miles, a motorbike can be the same as Trigger's brush, if you know what I mean.
I saw a "71" plate triumph yesterday with rusty shocks. I don't know it's millage and that was the only rust I could find. I had a Triumph Trophy 1200cc years ago. It was very clean when I bought it used and very clean when I sold it. I was very happy with the way it went, handled and in the time I had it nothing went wrong.
My next bike was a VFR750, I tried to get my mate to buy the same but he bought a Triumph (both used) , both bikes were very clean. I clocked up lots of miles on mine and nothing went wrong, it was as clean when I sold it as it was when I bought it however, my mate had a problem with his Triumph.
The Triumph was looked at by him and a local mechanic but ended up in the Triumph dealer in Plymouth. It stayed there for most of the summer while they searched for the fault and it cost him a fortune when he got it back.
I was talking to a chap who runs a motorcycle group in Plymouth who rode a Triumph which had done mega miles, I was impressed, during the conversation he mentioned that it did have a replacement engine during those miles, not so impressed.
I am not meaning to run Triumph down and they do make some great looking touring bikes but as to the reliability? What are the other options? I have owned 7 BMW's and know that the later ones, 2000 onwards are not as good as they look but I'm not sure about the 800's (I almost bought one some years and bikes ago.
If you ever feel the itch to buy a Triumph I should visit some biker meets and look at some that have been used, also try to talk to the owners to make sure they are not also a Triggers brush and ask the mileage and if it has been ridden in rain and salt.

Just my humble opinion.