The Monterey Speed Week takes place in early August each year. It has so many events it's just impossible to get to them all but there is something for every enthusiast. The historic races at Laguna Seca are unbelievable. Fields of 30-40 Can-Am or Trans-Am cars, etc, etc. Pebble Beach the same weekend can be expensive ($300 entry in 2011) but if it's on your bucket list then do it. This then gives you 4-5 week to get to Goodwood.
This is the 2015 site:
Monterey Car Week, Monterey, California, your only source for complete events schedules and local information.
The Moto GP is at Laguna Seca a week or two before Speed Week so if you want to see Jack Miller fall off you could include that. You might also want to check what's happening in Baja racing around that time - if I recall you have an interest there.
Do you need someone to carry your bags?