Yeah, what John said.
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The issue of what's "right", "wrong" or "enough" to do to an image in PS has been cussed, discussed and debated on almost every photo forum under the sun. The answer usually arrived at by consensus is pretty much - it depends.
For railroad stuff, I usually limit work to what I'd do in the traditional darkroom. Dodging, burning, contrast adjustment and so-forth. And of course, cropping. My preference is to do no retouching, other than to deal with things like dust and scratches, but that's just my personal preference, nothing more - I don't hold myself out as having the ONE TRUE ANSWER on the subject. In fact, as noted above I will gleefully crop to get offending objects out of an image, and there're those purists who find even that approach sacriledge.
Like John, I'd simply pass on shooting a scene which contains elements I don't like - unless, of course, it was a once-in-a-lifetime shot. Then, I might be tempted to grab that ol' clone tool...
There's always a "but, if...", isn't there?
As for people in shots, a lot of railfans seem to go overboard with their internal foamer-filters and produce rather sterile images in an attempt to get the whole train and nothin' but the train. Mark Bassett, over at the Nevada Northern, wrote a pretty good article on the topic a few months back in his "At the Throttle" column. Follow the included link if interested.
Nope, I don't like the guy with sixteen cameras hanging off of him getting in my shots either (and I'll probably be first in line when Russ markets his wonderful new NTFM filter), but his two kids staring in awe at the loc as it steams past can be magic.
And crew? Can't get enough of 'em. Even if there's a pole and a wire or two in there...
Scott