Thai people are usually courteous and a firm but polite no (mai ow kap for men or kah for women) usually works.

A busy schedule but a great country to try and get the most out of. Instead of Chiang Mai you could look at Chiang Rai which is a little smaller and close to the Golden Triangle.

When in BKK make sure you do the Temple Tour. We always did it independently as Taxi's are cheap and plentiful. Start at the Grand Palace (Wat Prah Gel), then Wat Poh (Maybe for a massage) then head Wat Arun to the reclining Budha and lastly over to Wat Arun on the other side of the river.

There is a great entertainment area on the river called Asiatic. It has restaurants, bars and a night market. A nice place to wander around for an evening.

http://www.thaiasiatique.com/index.php/en

A final suggestion may be to take your Wife on a dinner cruise up the Chao Prahya river. I would recommend the Shagri La cruise personally.

Hope that gives you some food for thought.