You're not wrong, but we still need to at least try to keep to an essence budget if we can. If we drop to 3 then we basically only have a single essence to spend before we have to choose between activating charms and being able to use Shintai.
Only way around that is to somehow take a bleach bath in the back of Gard's truck between fights or ask Michael to whisper a secret to us in the back seat. Both of which I'm reluctant to do with Marcone's goons sitting right there to take notes.
Budget is good. But false economy is something to guard against.
We currently have 9 Essence and 7WP.
We need 2 Essence and 2 WP for activating shintai, and say 2 Essence for 2x Melee Excellencies against Kattrin.
That leaves us a budget of 5 Essence and 5WP in the interim.
Im reasonably sure we're going to stumble across a secret or two between the store and the prison cell to trigger Essence regen.
If only because we're about to go into Undertown for the very first time, against a bunch of ghouls, then go through a warded door and brave a ghost or two.
And Im reasonably sure that rescuing Cindy will gain us 1 WP by ExWoD rules(acting to support or affirm an Intimacy, in this case both Dresden(Crush) and Michael(Love) )
Its also worth keeping the timeline in mind.
We finished talking with Gard around 1PM. Assuming 30 minutes transit time, it should be around 1.30 PM now.
Count another 30 minutes for preptime, breach and extraction.
This should be done by 2 PM unless stuff goes egregiously wrong.
Leaving us another six hours in the day before sunset.
We should also have warning from Ride if Kattrin attempts to use her car to go anywhere. Unless she uses a cab.
EDIT
1) Just occurred to me that Tool Constructs might be useful for breaching the wall of Cindy's cell.
Avoid the door.