Three very early stations come to mind. WDZ in Decatur, WEW in St Louis and WHA in Madison, remained daytimers!
A few other very early stations that never upgraded significantly:
Now dark (Original calls) KDYL-910 in SLC (910, 5/1 kw) is not, today, a viable facility. KWIZ (KFAW) in Santa Ana is a limited facility on 1480 in the large LA market, programming Vietnamese shows. KRE in Berkeley, CA remained a local Class IV after the act of 1927, never to change. Another low power stations that originated in the very early days was KGFJ in LA, a facility which is still a local channel operation.
Those are just a few examples. Stations got a chance to improve when the Federal Radio Commission reassigned frequencies in 1927, clearing the dial of many low power hobby stations, and creating the platform for the clear channel stations. A lot of stations, though, did not think that the perfectly adequate powers of 500 watts to 1000 watts then needed to cover even a large city needed further improvement.