Dilute Al-Er-Sc-Zr-Si alloys, strengthened by L12-ordered, coherent Al3(Sc,Er,Zr) nano-sized precipitates formed on aging, can be used for structural applications up to 400 °C. Group VB transition metals (V, Nb, Ta), due to their low diffusivities in aluminum and solubilities in L12-ordered Al3(Sc,Zr) precipitates, are used herein as micro-alloying additions to further improve the high-temperature service of said alloys. Alloys containing < 0.1 at.% V, Nb, or Ta are homogenized and subsequently subjected to various aging treatments (isochronal, isothermal, or double). Microstructural evolution during these treatments is evaluated via electrical conductivity measurements and micro-hardness tests, which demonstrate that the three elements significantly improve the coarsening resistance of L12 precipitates at 400 °C in comparison to an Al-Er-Sc-Zr-Si control alloy. The atom-probe tomographic analyses reveal that V, Nb, and Ta are concentrated at matrix/precipitate interfaces, indicating their partitioning to the outer layer of the nanocore/shell precipitates.