A Hohenzollern Spain after the Franco-Prussian War

If a Hohenzollern became king of Spain in 1870 and France also declared war on Spain, what might Spain gain at the Treaty of Frankfurt?

Corsica or frontier territory might satisfy prestige ambitions, while West African possessions are suggested as a more financially useful and supportable choice.

In this counterfactual, Spain joins Prussia in fighting France after a Hohenzollern takes the Spanish throne in 1870. Corsica, territory along the Franco-Spanish border, and colonial possessions are considered as possible gains at the Treaty of Frankfurt. The discussion distinguishes territorial prestige from the income and administrative burden of the acquisition. Corsica could cost money to hold, while West African territory is suggested as a more profitable option that Spain could support. Taking more Basque territory would also bring political difficulties. The choice could affect Spain's later financial weakness, though none of these gains is treated as inevitable.