I use the original Tamron 28-300 zoom professionally. I sell at least 5 photos a month to magazines, and no editor has commented anything but positively on them or asked what lens the pictures were taken with. I am not using any other lens at present (on a Nikon D1x) and for closeups, I am using screw-on closeup lenses which are inexpensive and effective.
The resolution is more than adequate even for two-page spreads, and most magazine photos are closer to 4 X 6 or even postage-stamp size.
I have no idea if this lens would be good enough for exhibition photos, but as I am not doing that kind of work, it doesn't matter for me. What does matter is not having to think about what lens I need. And not having to risk getting dust inside the body.