How likely is an average person to build a tolerance for wellbutrin (bupropion)? is it a lot like stimulants in that regard, or is it sustainable like ssri's?

Quite sustenaible: The Bupropion has sustainable properties, although after some variable time the dose might have to be adjusted in a few cases due to reduced response or a "poop-out" in long term treatment..

Good question: It generally does not show tolerance, however, that is a difficult question to prove. In most cases, I would argue the disease or clinical condition tends to vary in severity more than the medication or the medication's effect on the body. So the "illness breaks thru" rather than the medicine stops working.