How can i be sure my new dentists recommendations for more cleanings (3 vs 2/yr) & a new crown are justified; are there things i myself can observe?

Probably not...: ... unless you've gone to dental school. Your dentist is looking out for your best interests. At your age, it is not uncommon to need more frequent cleanings due to perio problems. Crowns don't last forever, either. You are always welcomed to get a second opinion from another local dentist.

Dental cleanings: Some of the factors that determine the frequency of dental cleanings are swelling, redness, bleeding gums, amount of plaque and tarter, amount of bone loss, pockets, smoking, dry mouth, your systemic health and medications you are on and others. This is quite common as one ages. Ask the dentist to explain the recommendation to you.

Second Opinion: Sometimes having a second opinion is helpful and gives patients the confidence and comfort they need to know they are making the right decision. Good luck!