What is the alternative today for restoring rights to their rightful owners, in light of the Arab regimes that plunder the peoples' wealth and do not pay zakat to the poor, by analogy with Abu Bakr's war against those who withheld zakat?

Stolen and usurped money is not subject to zakat (definition), and must be returned to its owners. Abu Bakr's fighting of those who withheld zakat was in his capacity as a Caliph, and individuals are not permitted to do so. The injustice of rulers is a reprehensible act that must be denounced with the heart and tongue, within Sharia (definition)-compliant guidelines. It is permissible for someone who fears for himself to remain silent, while still denouncing it in his heart. If rulers fall short in collecting zakat, then individuals must disburse it to those entitled to it. Whoever is able to remove injustice or restore rights must do so.