We'll be staying in Evora, Portugal in mid October and considering a side trip, including dipping into Spain.
Any experience or recommendation for a day visit in Badajoz?
To me, Badajoz has no “must see” sights. It would be good for walking around and relaxing. It does have an Alcazaba and an interesting bridge. If you like Roman ruins, then continue past Badajoz another 30 minutes to Mérida. It has an abundance of Roman ruins.
And what about Jerez de los Caballeros and Zafra?
Zafra is very pretty around the main square, but it is a fairly quick visit. I probably would not want to drive two hours each way just to visit Zafra. It would combine well with Jerez de los C. in the same day, but I have never been there so I do not know if it is worthwhile.
Not in Spain, but slightly closer to Evora (1.5 hours), I would consider Marvão, popping by nearby Castelo de Vide as well.
Otherwise, the most "obvious" destination on the Spanish side is indeed Mérida.
The Zafra suggestion on the Portugal forum was if you were going to make a loop heading east from Evora to Jerez de Los Caballeros and Zafra, then working your way north and returning to Evora going through or past Badajoz.
The Badajoz, Mérida suggestion is if you didn’t want to visit Jerez de los Caballeros, Zafra, and the castles, and wanted to go directly to Badajoz.
Jerez de los Caballeros Is a 1.5 hours drive from Evora, while Badajoz is a 1.25 hours drive.
Which you decide to you can wait until you’re there depending on weather and how you’re feeling. It would be easy to spend a month in that part of Spain.