Like Glass said, Glock discontinued OD frames last year when they started releasing the Gen4s. Some people now see them as collectables and will pay more. Your models are popular so probably in demand. It's up to you whether to sell them now or hope they go higher in price. Hard to say since you never know what someone will pay for "unique".
You could keep one and sell the other to straddle the fence. There's little benefit to the new 27Gen4, it's roughly the same as the older 27s but I think there's a big difference in the 23Gen4. You might want to check both out in the LGS and then decide what to do.
This is a little like 1941/1942 Lugers with black bakelite grips. These models came from the factory with plastic or wood grips and for a long time no one liked them with plastic so replaced the factory grips with wooden ones so their Luger looked "right". No one wanted the plastic grips even though they were original. Of course being separated from the gun over time those grips got lost and rarer and rarer. Then someone started calling the remaining samples "Black Widows" and boom, those Lugers are worth $500 more! Everyone started scrambling looking for original black grips for their byf 1941 or 1942. Then fake plastic grips came out, all adding to the mystique of the black widow. So the price keeps going up.
Could this happen to the OD Glock or is it temporary? Who knows? I'd probably sell them now and get Gen4s if you find the Gen4 better for you. Look how long it took for a different color grip for the Luger to skyrocket.
Of course a catchy name might do it, so invent one now, don't wait!