Just keep in mind that regardless what you buy in aluminum shouldn't be something that sticks out that will make first contact with the ground on a jump gone wrong. Even good brands bend or worse, rip other parts off your truck while bending.
Towers/arms should always be plastic, at least for a basher. It's easier to replace a tower or arm than it is to replace a bulkhead and bent hinge pins due to alloy arms or a bulkhead with the top snapped off due to the aluminum tower not giving.
Center skids are good as alloy, front/rear ones, not so good if they are to act as bumpers. On the revo rear, it's almost a necessity unless you like replacing the stock one frequently due to it wearing through.
Bulkheads, diff cases, diff collars, servo skids, trans cases and servo arms, things like that are good as alloy due to them not taking direct hits. With those pieces, your relying on the alloy's shear strength and lack of flexibility to keep gear mesh true and bearing seats from getting sloppy due to heat.
Sorry... rambling.