Actually, the S7 is not critical at all since it has probably none of the parts I want - or at best, very few - for this project.
The parts that come off an S1 or S2 I might prioritize higher when I've exhausted my own stock. I don't have any S2 boards to part out (all mine are museum) but I have enough S1 boards to provide caps for 50 pods. I'll burn through those, but 30x S2 boards would run power for over 100 pods. However, an S5 board provides about 5 times the value in parts I'm short on compared to an S2 board (when component cost is considered). The design has changed a bit such that the S1 and S2 now have more valuable parts than I had originally assumed so they will be prioritized a bit higher.
However. Only trading pods for the hardware required to make more pods is not sustainable.
Only about half the cost of the pod is recycle parts, so for every pod that goes out in trade for hardware I have spent a decent number of dollars which did not come back. Additionally I spent a lot of time pulling, cleaning and readying parts for assembly on something new. I know a lot of people will be paying money for pods, but a lot of other people will not. If I don't keep a practical ratio on things, I'll end up with a whole lot of parts I can't use and a lot of PCBs I'll get ten cents a pound for and will have basically paid a lot of people to take my miners. Unfortunately, I can't trade old PCBs for sandwiches at a very favorable rate, nor can I pay the rent with them.
You can't just send me parts and assume I'll send a miner back. I will not send a pod to anyone, no matter how many boards he ships to my door, without having agreed upon the terms of the transaction first. The agreement will be based on the availability of parts I already have and how much I value the parts being provided at that moment, which means that at different times different boards will have different values because I'll need them more or less than at other times. If I find that I have enough boards already on hand to build every pod I feel like putting together ever again, I'll stop taking trades entirely and only sell for money (or other things which I find interesting or worthwhile, surprise me).
How about a combination thereof?
You need parts, but you also need money.
PCB's don't make for very good snacks, that much is understandable.
For instance i could offer a combination of one dead S5 board + some Working S1 boards + some money, if i was to get several miners back, i could get a significant upgrade over the S1's i'm running now and you'd be making miners out of the parts i gave you(in equivalence) + some from you + you'd also have money to cover your time.