I bought the RS France 2012 but there is no mention of Nimes. In other books this city is highlighted for its many Roman artifacts/sights. Is this a good way to spend a day? We are staying in Avignon for 4 days.
There's no mention of Dijon, Marseilles and many other cities in the France book either. We ran into the same situation. And, we rented our car in the Nimes train station so that we could drive out to the Pont du Gard. And, we turned it in in Dijon. Fortunately, we also had our Frommer's book. Both worked out well.
The RS Provence And The French Riviera book has a section on Nimes (and Marseilles). Nimes was my favorite of the cities I saw in that area. Others were Avignon, Arles, and Orange, and the last two were especially worthwhile (Avignon was OK, but I preferred the others).
Yes, Nimes is very interesting. It is convenient to combine with a visit to the Pont du Gard. Areas you did not mention, but very interesting, and day trips from Avignon, are the Luberon Hills and Cote du Rhone areas.
I do find it odd that the France guide doesn't so much as mention Nimes in passing. Rick did highlight it in on one of his television programs, though.
As Harold mentioned, the Provence book does talk about Nimes. That is why there are regional guides that get more in depth. Can you imagine how fat the France book would be if it included everything?