I spent about four days in Seville. Its WHS may be seen within a day but the city has a lot to offer beyond the splendid Alcazar and the cathedral and the less interesting Archive of the Americas. One morning I took the bus to look at this tentative site. I missed the bus at Plaza de Armas since the bus stop is a bit hard to find among the many bus stops in the very north of the square and hidden around the block. I took the next bus half an hour later. Since you are leaving the city all day tickets for the city are not valid on the bus to Saltiponce but the fare is cheap. 

In short: the site is worth a visit but no must and certainly no WHS material. The site offers a very small museum, I assume most objects are in the Archeological Museum in Seville (closed for renovation) and in the splendid Archeological Museum in Madrid. The site offers mainly two things: the pop-culture-famous amphitheatre which is an impressive ruin but certainly no match to already inscribed and much better preserved amphitheaters in Rome, Arles and the not inscribed Nîmes theatre. The second attraction is a series of nice mosaics as part of excavated roman villas. There is one with clearly identifiable birds, one with the seven days of the week and their gods. You can spend an hour or so walking around the ruins. If this was the only Roman ruin on the planet it should be certainly inscribed but it is so much weaker and smaller than most already inscribed Roman sites that it wouldn't add anything to the list. The Spanish roman sites already have a rather weak inscription with Tarragona which has certainly more to offer. And there are several Roman sites that really should still be inscribed - Jerash and Bet She'an come to mind first - that Italica is fine as a side note for the history of Seville.

I visited also the highly praised Mudejar monastery of San Isidoro del Campo but found it rather neglected and a challenging mix of many styles. With a car it is certainly easy enough for a short visit, by bus I found it involved too much walking and waiting for what you get.