Thirty-two years in business, although I can shoot for the sky, I'm going to try to keep it down to earth, things you can do without too much code modification.
#1. You've heard this one before, multiple billing addresses under one account, B2B companies use purchase departments and these purchase departments could have credit cards throughout the country, in other words multiple billing address. This falls under the previous topic, let an address be an address.
#2. We have already introduced an order locking mechanism, in other words after 30 days, and a few days extra out of courtesy for returns, we lock our orders, not even an administrator can make a change. All you can do is print, if you want to make a change, you need to unlock a specific field in the database. We lock automatically using a query that checks for anything after 32 days.
#3. I noticed you want to manage invoices, this is a terrible idea. Concentrate on the shopping cart aspects, and let QuickBooks or some other accounting program handle this. No matter what you try to do, it will never come close to what a real accounting program can do.
#4. With all due respect, your security structure is just awful. An example, how can you have an order admin and not be able to go into a user account to either create a new user or modify an existing one? As a developer, we were able to modify the two files necessary to allow this, but for a regular user, this is a real pain. Maybe you can create a nice checkbox wizard that can automatically create the two XML files needed for security.
#5. I love the price value based on customer groups or customer roles.
#6. You probably are not aware, I fall under certain MAP pricing for certain products, would be nice to have an option that says, view all MAP pricing when logged in, or give me the ability to turn this on per user or user group.
#7. We don't use your inventory control, we do it outside the system.
#8. Manage purchase orders, very interesting, we added two fields to the order line items table and can manage purchase orders using Crystal reports today.
#9. Ship-station, well, it works today, but it would be nice to support multiple packages that can retrieve multiple tracking numbers. At the very least, be able to return multiple tracking numbers, even if it gets included only in one package.
#10. Would love for a coupon code to work after the fact, in other words, let an operator in the backend enter one after an order insert.
These recommendations are more down to earth, I have pretty much been able to work around any limitations of the system without reinventing the wheel.
Although I think that Zapier is just OK, is anyone really actually using it? I think that better add-ons from Ablecommerce would be a good start, again, just check to see what your competitors are up to.
I hope this helps