Ideally yes, once you unlock an item you should be able to place it as many times as your budget can afford. But if they are committed to the stock approach, a good middle ground solution would be being able to buy already unlocked items from the Decor Catalog UI. Having to leave my house to go hunt a vendor/AH item completely breaks the flow of housing.
If they dont do this, the only viable way will be having one alt parked in front of every single decor vendor and relog a million times, which needless to say sucks a lot