Subtle Spell
Silent spell, as is, has very limited uses. If you happen to come across one of the very few enemies that use silence, or you want to do some sort of PVP tactic where you silence yourself and enter melee with an enemy mage to shut them up.
Otherwise it is mostly just useful for spell slot management, but now quicken spell is a better tool for that.
Suggestion: Change Silent spell to be -Subtle- spell. Subtle spells do not have any animations/chants and do not show up in the combat log. They still have their full VFX/SFX. For example you can cast call lightning without moving at all and lightning bolts will simply fall from the sky, but if you cast scorching way then suddenly beams of fire will erupt from you.
I think this will add a lot of RP opportunities, especially to druids and shamans for manipulating natural forces.
Auto Silent spell should still only silence, not subtle spells.
Alternatively subtle spell could be a new feat that requires both silent and still spell feats, gives the benefit of both plus the above and bumps spells up by two levels like empower, instead of one.