My grandparents had a small orchard of those back then, just by where my house is now. Most were removed, but a single tree still stands.
I'll agree about lack of water causing small fruits, but your tree looks quite healthy. Valencias are strong. They also make a very "classic" tasting juice.
Every tree is different, but they do seem a little paler then I'm used to. Perhaps if you'll give them some more time they will get sweeter, it's a late season orange, and can hang a long time on the tree unharmed.
You can juice them, then cut the peel to strips and candy those. Seeds shouldn't be a problem in this method. I'm a fan of candied orange strips coated with dark chocolate.
If juiced before cutting, it will also be easy to be made into marmalade. And they can probably make some really nice liqueur.
You can also dry them if you find ornamental use in those.
