I do not think that Schwetzingen has a good chance, the ICOMOS evaluation says that "the comparative analysis shows that properties with similar values to those of Schwetzingen are already inscribed on the World Heritage List" and "This is patently a complex of high value at the national and European levels; however, it does not achieve outstanding universal value in areas already well represented on the World Heritage List."
That's also my opinion. A decision in favour of Schwetzingen would open the door for many more European castles, monasteries etc.
But the palace is very close to the motorway and if you like parks, it may be worthwhile to stroll an hour or so through the nice Baroque and English landscape garden. I would skip a tour through the palace itself, there's nothing exceptional.
If your time is limited, I would prefer to visit the other WHS in that hotspot: Völklingen ironworks, Maulbronn Abbey, Speyer Cathedral, Lorsch (a tour to the interior only takes 30 minutes), Messel pit (there is a new visitor center, but I would recommend to take a guided tour).
If you are planning further ahead (about 10-15 years or so), I can recommend a visit of the Mathildenhöhe
They make a bid for the German Tentative List for the years 2015-2030 and have a good chance, I think. Also for the final inscription in the WH list.