Of the Imperialistic Leaders, Genghis and Cyrus are the only ones that hosed by the 'settler boost' half of the trait. Cathy, Vicki, and Julius all start with Mining, so they are able to immediately take advantage of the

boost. Many strategies rely on beelining for Bronze Working (the settler boost also applies to chopped

).
I find that even at Monarch level, where competition for city sites ramps up pretty quickly, Imperialistic Leaders help me get better sites, by shaving a few turns of each settler. Especially Cathy, who also enjoys the border popping Creative trait.
Ideal example:
* Settle on a plains hill (2

in city square)
* Build queue Worker, Warrior, Settler
* Mine plains hill (4

) while building Warrior
* If you've grown to size 2 while building the Warrior, you can work the city center (2

), the mined hill (4

) and either a grass forest or any 3 food square for one more food/hammer towards the settler.
* Those 6

become 9

plus the extra

/

makes 10 total production towards the settler which means you can build a settler in 10 turns at size 2. That settler would take 15 turns for any other leader, giving you a precious 5 turn head start on any other leader.
* That 5 turn advantage is one border expansion for Cathy's newest city

* That size 2 city can now pump out another Warrior/Settler pair in 13 turns.
Note that this is dependent only on one Tech: Mining.