I have two weigela bushes that are in the second spring/summer from first planting them. Should the light pruning after the spring blooming period be to cut back all the flowers, or cut some of them in order to give them a more defined shape?
This depends on how large your shrubs are and if you need to shape them.
If the size of the shrub is fine right now, just dead head the flowers.
If you need to shape up your plant them go ahead and make those pruning cuts after blooming.