Andalusia Itinerary - need to fill 4 more days

I'm assuming that when you write "days", you really mean "nights", so the listed durations overstate the time you'll have in each city.

Four nights is the minimum I'd recommend in Seville, and I think you'd benefit by having an extra night there.

Ubeda and Baeza are very worthwhile; they're architecturally quite different from the other places on your list.

You could add a day to one or more of your bases to allow a day trip to:
Carmona (from Seville
Vejer de la Frontera (from Cadiz)
Priego de Cordoba (from Granada)

All of the above are accessible by public transportation but are not on express-train routes.

Given that you might well still be jetlagged on your first full day in Spain, I don't think it would be a terrible idea to have a third night in Malaga.

Okay, got it. You are not counting nights. This is what is looks like to me:
Day 1 arrive in Malaga quite late and jetlagged.
Day 2 pick up car (what time to they open?), drive (1.5 hrs at least) to Gibraltar crossing, find parking, 1/2 day sightseeing. Then drive (1.5 hrs at least) to Cadiz.

Day 3 Cadiz full day
Day 4 drive to Ronda, stopping along the way in hill towns
Day 5 1/2 day sightseeing in Ronda. Return car and train to Sevilla ??? Makes more sense to drive to Sevilla and return car at the train station. Then short taxi ride to hotel. That way you can see more of the hill towns and lovely vistas.

So that's your first 5 days. You've stayed in 4 different hotels (5 if you plan to sleep in Gibraltar) and you've only had 1 full day of sightseeing anywhere. And that's while your body's still adjusting to the time difference (i.e. circadian rhythm). I would be exhausted by that pace. Which is often the main reason I urge people to count nights rather than days, so they can get a better idea of how much time they'll really have at each stop. If you like this pace, at least consider rearranging the itinerary so you have 2-3 nights at your first stop after Malaga. For instance, you could train to Cordoba, then Sevilla, then car for that part of the trip and end in Granada.

One more thing to think about is that many Americans have trouble getting accustomed to the evening dining hours in Europe. In Spain they are even later, usually beginning at 9 or 9.30. To manage, they adjust by eating their main meal at lunch - which eats into sightseeing time. Sure, you can find plenty of places to get light meals, but good dinners are hard to come by any earlier.

I see. I should have specified nights in the above schedule.
Malaga - 2 nights
Gibraltar - 1 n
Cadiz -2 n
Ronda - 2 n
(return car)
Seville - 4 n
Cordoba - 2 n
Granada - 3 n

With 4 extra nights, I'd add one to Gibraltar so I could do a day trip to Tarifa, one to Seville, and 2 nights in Nerja.