My mom is 81 and had the same thing after a small stroke two years back, and her OT said 15 minutes a night is the sweet spot, anything more just tires them out and the writing gets worse. The thing that made it stick for her was adding a little resistance, like signing actual checks and writing thank you notes by hand instead of just copying words out of a notebook. Copying is one thing, but your brain has to care about what you're writing or the progress fades fast. Her handwriting held up fine for about six months after she stopped the exercises, then it got sloppy again, not shaky like before but just lazy, so she went back to the notebook three nights a week and it tightened right back up. That tells me it's less like a broken bone that heals and more like a muscle you have to keep using. Worth asking his OT if they want him doing something with purpose, like the birthday cards, instead of just grocery lists. The fact that he wrote that card without thinking about it is a really good sign.

Tried the cash thing after my girlfriend dared me and I walked around for two weeks feeling like a drug dealer with a wad of ones in my sock drawer. The dumbest part was realizing I'd been dropping $9 on coffee and a muffin every single morning without blinking, but handing over a ten and getting one lonely dollar back stung way more. Cash makes you feel the loss in a way a card never will. I still keep rent and utilities on autopay because missing those would be a real problem. The fun money is all cash now though. Call me old fashioned, it just works.