I'd say, treat it just like you would other plumbing. You wouldn't run water in an outside wall without special consideration. Inside walls or ceilings, no problem. You don't worry about water pipes developing a leak in 5 years, why worry about an air line? In fact, it's potentially easier than copper plumbing in that you can run a continuous air line if you use either pex or air tubing from Goodyear, Graco, etc. with no internal joins/splices. Now it's safer from accident just like water lines are.
To me though, it would be a matter of appearance and cleaning. If you did a beautiful job with copper all polished and laquered, or iron done in glossy black and made it a design point, that would be one thing. Otherwise, it's just another thing to collect dust, to remember to take care when near/don't lean things against that pipe, etc.
And you can check with engineering types, but I believe that it's very difficult for rubber or pex to condense on the outside, and you DO want it to condense on the inside of the tube/pipe so that it can drain to low points where it is collected by traps/filters instead of running through your tools and condensing there. Higher quality set-ups specifically run the warm air through a refrigerated unit to get the air to condense out its moisture.
