A few things to keep in mind, then. I don't know what the chances are that your chosen vocation will allow you use of a CIRAS, but I suspect the chances are low. Many of the "gunfighter" rigs take various specific cuts of soft armor and aren't designed to work with anything else. There are as many different sets of armor as there are different armor carriers. (RAV, CIRAS, FSBE AAV, Interceptor, etc) If you're not yet in the USMC, perhaps by the time you will be in a position to use a CIRAS, something better will have come along.
Nevertheless, on the flip side, as long as you're intelligent about it, most higher end gear items hold their value very, very well. I sold my CIRAS for about $10 less than I paid about 8 months after I purchased it. That may be an extreme example, but certainly 75-85% value retention is not uncommon if its in good shape.
Of course, I don't know much about the Marine Corps, but based on what I do know, I would suggest you not consider the CIRAS as something you should purchase with professional use in mind. (At this point, anyways.)
As far as a viable "excuse" to buy one for airsoft, with the caveat that you can sell it at perhaps little loss later, I suppose its alright.
