The old town of Cáceres has a lot to see. In fact, it's on the UNESCO World Heritage list... and that's for something.
The church of Santa Lucía de Trampal (in Alcuéscar) would be another not to miss sight.
If you made a Vía de la Plata plus Sanabrés mix, the church of Santa María, in Tábara would be another not to miss sight.
Other interesting places along the route (in addition to those you already quoted on your original post): Santiponce (with the monastery of S. Isidoro del Campo and the ruins of Itálica), Zafra (several convents, a colegiata...), Villafranca de los Barros (church of Nuestra SEñora del Valle, the former flour factory -nowadays a municipal cultural center-) Almendralejo (the palace where writer Espronceda was born, the Teathre-cinema Carolina Coronado...), Galisteo (walls and church) and the Roman baths of Baños de Montemayor (
www.villatermal.com/index.php/component/content/article/2-uncategorised/302-termas-romanas). Of course, this list is far for complete as you'll find more interesting places along the route (the churches in some villages/towns, the albergue in a former palace in Torremejía and so on) but I think some
suprise element isn't a bad idea.
If you are going to continue on the Sanabrés, Puebla de Sanabria, Lubián (with the Santuario da Tuiza and the castro das muradellas), the Oseira Monastery, the colegiata de Xunqueira de Ambía, Ourense...