Dude, completely disagree. The double attack or attack/move is huge whether attacking a city or a unit.
Double-attack is straight forward enough, you can attack a unit twice or a city twice, nice.
Attack/Move you are way undervaluing. If you attack an adjacent target and don't win, you can move away allowing a fully healed unit their turn. On a city in particular this is huge. If it has only 3 attack tiles and you have 6 units, all 6 units can still attack at full health. That is an insane bonus.
I agree with you. And the great thing about double attacking riflemen is that if you want, you can attack/move with them instead. Thus for a city with 2 accessible tiles which are both plains, you can attack with 4 full health rifles by attack moving.
A funny thing to see is double attacking EMBARKED riflemen with amphibious.
Move/Attack/Attack
or after steam power
Move/Move/Attack/Attack
or Attack/Attack/Move + Move/Attack/Attack