That's a good looking boat Strobeguy. I have a 590, the little brother to yours. My boat, while just for personal use, gets a lot of heavy use and has been bombproof. A big advantage of the 640 over the 590 is the second inboard fuel tank, which is great for range and also weight distribution in heavy weather.
My tubes are upwards of 12 years old and in perfect shape. UV light is what kills them faster than anything. I have been "religious" in keeping my boat tarped when it's out of the water, which might be impractical for you, although if you are "north-ish", it's not as big a deal as if you were "south-ish". You will likely end up with a pink-ish orange boat before too long however!
For what it's worth, if I was replacing my boat today, I would go to a 640 but would power it with twin 90s. (This would follow my lottery win of course...)
I don't think I've ever used so many "-ish" words before!