I think your plate prices are very reasonable, and you've ran 4 rounds already, and from the pictures of R4, all the plates look excellent, I would based my buying decision on that alone!
As for the PCBs, I wish they could be a bit cheaper, but I understand this affects your margins. Maybe introducing tiering based on numbers purchased? I'm happy with your decision to have one neutral coloured PCB and one vibrant one, planning to get 2 sets for round 5.
As for what I want to see in the future, maybe Alps 60% plates?