Change it. The transmission fluid is basically 10W-30(? or similar viscosity) engine oil with additives in it. As with any engine oil, it not only breaks down with use but also with time. It's so cheap that there's no real reason not to change it. I've done mine twice in 25K - overkill, but I wanted the new Honda synthetic fluid. Make sure you use Honda brand and make sure they give you part number xxxxx-9031. The old part number -9016 is dino oil and -9031 is synthetic and they cost the same.
I don't think it's necessary to flush it, however if done properly it will not cause any harm. Most "flushes" are basically pumping used transmission fluid through the tranny with a machine - this is the bad kind. The kind you'd want to do is: drain/fill, drive for a few miles, drain/fill again, drive more, etc. I personally don't think this is necessary as mine has always come out looking pretty darn clean.
