Yes, I've worked several such bases near me. There was a proliferation of bases blt. during WWII, Korean, and vietnam era, as you know. And yes, some are now decommissioned, or very minimally used, or abandoned even, and/or being turned over to city's nearby them, etc...
They are good to detect for silver (although you won't find anything spectacularly old, if they only date to WWII-ish). The reason they're good for coins is, the military men had their canteen money. And their baggy BTU's (with the sideways pockets) were good for loosing coins. And of course, all the PT courses, etc....
The best spots I hit on our close-by base, were the older military housing unit yards. Sometimes a postage stamp sized yard would have 100+ coins in it! (mostly clad, but some wheaties and silver in each). I guess for those guys coming out of the depression, to have a steady job for the first time ..... they must've come home and generously passed out the coins to their kids, haha. Another place we have fun doing: is to rake out under the porches of the barracks, if the porches are those wooden veranda type. Apparently the men would sit on the porches during their breaks, to smoke, play cards, etc... If the slats between the planks was wide enough, coins would go through. Some were sterile (cleaned out in the past, or no gap between the slats, etc...), but sometimes we'd hit a good one with a lot of coins, old military rank medal things, etc....