It would be nice to have a built-in negative condition for the discounts. For example, customer is NOT in role 'Wholesale'.
We would like to apply discounts for Guests and Regular Customers only, but all registered customers must have the 'Registered' Role assigned. So there was no way to make the Discount apply to Guests and Regular, Registered Customers, but NOT Wholesale Registered Customers.
I was able to work around the issue by creating a New customer role and assigning ALL Regular(non-wholesale) customers to it. Then I could apply the discount to Guests and the New Role only.
The only catch is that for new Regular Customer accounts to be created, it must be set to 'Approval by Admin first'. And at the time the Admin approves the account, they MUST assign the new customer to the new Role.
So if you need automatic/instant account approvals then this approach wouldn't work without some custom programming.
If there is something I'm missing here, please let me know. This is my first NOP project...