Sculptra in my Hands

Sculptra is good at adding voulme to the soft tissue.  It works well in the face.  It can work well in the hands.  Most would go with Radiesse as their first choice.  Talk to your experienced injector about your individual case.

Radiesse is a better choice if you feel you need to do something. You'll have instant results that work very well to plump up the area on the back of your hand. By creating additional volume, you raise the surrounding skin so the veins are less obvious, but you will still be able to see them. Radiesse is long lasting and the injection and smoothing process is very fast (see video).

Why the blood vessels in your hands seem more obvious in summer:

When your body heats up, from environmental heat or from exercise, your blood vessels dilate, so you will notice them more in the summer or after exercising. People who exercise a lot tend to have larger vessels as well.

I would recommend Selphyl instead because it is more natural and results are better. But you can try a short lasting filler like Restylane. Best of luck.