I am several months into the self-hosting journey and I feel I have outgrown my Pi 4 B 8GB. I’m only running around 3 dozen containerized services and it seems to struggle to keep up. But I’m not sure of the best bang for my buck. I’d like good, long-term performance, but I don’t really have a grand lying around for a Lenovo Tiny or Dell Optiplex or ASUS NUC. I’m thinking of buying an SSD to boot from, but will this even help much? For $350-500, could I make a more cost effective homeserver upgrade?
Pretty much this. There is a significant learning curve to kubernetes (or similar, I guess?), but it’s a handy skill to be familiar with. If things basically run but with degraded performance on one raspberry, there is no real need for a vertical performance increase. Adding the second will provide almost double capacity, with some HA added for fun.