If you are planning to stay in Chiang Khong for a couple of days before you cross the border (which I would recommend), Baan Sakuna Hotel & Resort is one of my favourite places in Thailand. Happy trails.
Any effect will be marginal, and probably only barely noticeable in the already busy tourist areas (which I tend to avoid). The more dominant change will probably be seen in the 93 countries / 60 days visa exemption numbers. We’ll have a better indication in a few months, when the arrivals trend data is published.
Fine or not, I would never exceed the 59 days limit. (various countries’ arrival documents ask “have you ever over-stayed?”) Harsh I know, but if your wife’s Aussie passport got stamped with an expiry date, I understand their very strict application of the over-stay rules.