1. You could "hibernate" rather than shutdown that would eliminate the load time when you press the "Nav" button although your GPS reciever would still take a minute to lock on.
2. Hibernate would also help you here but you will still have a bit of load time for SD
Lastly I'd recommend running StreetDeck using EWF and HORM see this post if interested.
Instructions on setting up EWF and horm http://granturing.blogspot.com/