"Incredibly" valuable. Not anymore, they're common goods now. I bought a USB GPS module on Aliexpress the other day for a couple of USD. GSM modules also exist for USB. Virtually all of them run proprietary firmware. An old SoC is not very valuable, if you consider say Raspberry Pico and what you can do with such. The best thing to do with an old smartphone is IMO to recycle (= mostly downcycle) it. It still contains some valuable metals like cobalt and gold.