Can anyone help or direct in dating this Union Serviceman's Carry Tool Box?
It's almost certainly immediate postwar through late 40's, not much later.
A number of us here, including myself, d42jeep, and Username already in use, have several of these style boxes from WWII, including Union made. (Other mfgrs include Hamilton Metal Products and E.J. McAleer.) They are the box that all the wartime GMTK's (~110 pieces, 65 lbs) were carried in. At first glance, except for the bluegreen finish, your Union has all the signs of a WWII box, including the feet (corner supports), which you don't normally see on postwar civilian boxes. But wartime Union boxes only had 33 hinge elements. Is there a hole in the removeable tray for the push-bottom oiler spout to poke through? That was typically dropped postwar as well.
I have a question though. If you're not already familiar with all this, why are you calling it a Serviceman's Carry Tool Box? Is that actually on the label somewhere? If so, that's pretty cool. It would reflect Union's immediate postwar marketing plan.
On your other questions, I wholeheartedly agree with everything everyone else has said. My inclination is to always preserve, if possible. If not, then restore. Making the decision is sometimes hard on the "'tweener" boxes. Not too far gone, but not great either. When I decide to restore, my philosophy is a little unique in that I don't like to restore to mint/NOS condition (which almost never matches the condition of the tools), I like to restore to well-used, well-maintained condition, and I go so far as to add wear and tear and patina with techniques. You can see a Hamilton WWII box, as well as a Plomb and a Snap-on that I refinished this way in a GJ thread I have on that subject linked
here.
EDIT: In fact, if you click on that link and go to Page 2 and the last post, you will see a Williams Bantam (3/8-inch drive) socket set box that is a good example of a dilemma box. The lid is in very good condition for a 70+ year old box, and the original decal is excellent, but the bottom is roached.