The only sites I've used in the Valencia area are those at Navajas some miles on the road to Teruel and that at Moncofa on the coast around 20 miles north.
Navajas is a nice site in an interesting small town, but is not suitable for long outfits as the upper site roads have sharp corners bounded with stone walls about a foot high ideal for hitting the bottom of the caravan. The pitches are level and reasonable size but the road between them is steeply uphill such that one side of the pitch is level with the road but the other has a step of up to about 7". (I hope I've explained this. As you stand in the road facing the pitch, the edge you have to tow or mover over is wedge shaped and you may not find it too easy. On a lower terrace there is a level area around the tiolet block but this is under trees and does not have the good views you get at the top. It also attracts families with young children to be close to the facilities. It can get very cold early in the year. All the water system froze one night in January we were there and we all had to leave.
The Moncofa site is near the beach and has some reasonable pitches. We stoped for one night and despite protestations had to pitch in the statics area which resembled an untidy caravan breakers yard. There were plenty of much better empty pitches elsewhere, but reason did not prevail - and it was very expensive. You will undeerstand we shall not be trying it again, although others will probably say it is fine.
There is a large resort site just south of the city but I have no knowledge of it.
The majority of snowbirds tend to stay either further north up the coast or further south towards Alicante. We go much further south towards Mojacar.
If you are going to south east France and down the coast you may find the middle of France very cold and even snowy at that time. We go down the west coast of France with stops south of Niort and perhaps near the border at St Jean de Luz (La rouletta site is easy to find and pretty good). Then via Pamplona to Sabinan north of Calatayud where the Sabinan site is open all year, clean heated toilet block, quiet and secure. Then via Valencia all the way down to Mojacar - a long 420mile day but very easy driving between Christmas and New year as there are hardly any HGVs on the roads. I'm no knocking the HGV drivers - most of them are excellent and helpful, but the sheer numbers on the roads into Spain can lead to fairly low average speeds.
Other popular open all year sites in France which may be of interest are Fururiste near Poitiers and at Orcet just south of Clermond=t Ferrand.
Hope this helps.
I
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