I am searching for some good reference tools or guides for the caregiver that address how to identify potential problems that may need medical attention, and the urgency of which medical attention should be sought. How can the caregiver become more observant in looking for signs/symptoms or changes that would result in seeking out care, and how does the level of urgency for that care established?
Try
http://www.nlm.nih.gov/medlineplus/seniorshealth.html
you can search this site for info on specific symptoms, etc.
From my experience, it is important to find good doctors that will take time to respond and that your parent likes before a crisis arises. A doctor that will return phone calls and will work with the patient and family. Also preventive care, keeping them from becoming depressed, or sedentary, from becoming dehydrated, from not eating properly. Make sure they address health issues before they become worse, montitor side effects of medications. Watch for symptoms of urinary infections, vitamin B12 or D deficiencies and not having regular bowel movements because these problems can cause all kinds of problems in behavior and health. Get them regular dental care and keep their ears cleaned of wax. Make sure they are able to do things like bathing safely. The above are all things I never thought to monitor as my family member aged. Suddenly you have a health crisis and have to learn all the above the hard way.