It would be very helpful if the checkout rates provided through the store connection had support for conditions. In our case, we always insure any orders that exceed a certain value but the added cost of insurance cannot be provided through the store connection checkout rates. This means that for any high value orders we receive, we are footing the bill for insurance. If we could have a conditional for our checkout rates that basically says "If the order exceeds x value, add a flat fee of y dollars" or something similar that would suffice. If it actually calculated the added cost of insurance that would be even better.
I believe this would improve the open-endedness of Shipstation and would benefit other businesses selling a diverse product lineup including products of lower and higher values.