As long as he's not physically hurting anyone, I'd be inclined to put up with it. But I would be concerned for his safety - it looks like you live on a fairly busy street. I'd hate to see him just step out in front of a car.
Dementia/Alzheimers is a horrible disease to watch. I'm having to watch my mother decline right now. Fortunately, she's "pleasantly confused" and not one of the victims that turns angry as the disease hits them.
Back to the thread topic of "dented cars"... About 2 years ago, my dad went through a period where he was "running errands" all the time in the car. One day he left the house at 8:30 a.m. - without his cell phone - to run errands. I was a little concerned, but not too much, when he wasn't home by mid-afternoon. Around 5:00, I cruised around his normal spots, but didn't see him. At 8:30 pm, I called the local police. They told me that they'd found him earlier - with a flat tire - and had him towed to a local tire shop for a replacement. The tire shop replaced the tire and sent him on his way at around 8:15 pm. GREAT - he's on his way home. Never showed. I called the police again around 10:00 and filed a missing-senior report. At 1:30 a.m. I got a call from the local ER. After leaving the tire shop, he decided to "explore a bit" and put about 100 miles on his car before driving up the main street of a little town about 40 miles from here. He was going fast enough (in a 25 mph zone) that after he hit a parked GMC Envoy, he flipped his Subaru and traveled about 75 feet on the roof of the car. He basically walked away from that "accident" with a small cut on his elbow. Fortunately no one else was hurt. Needless to say, I took away his driving privileges - so now I'm the bad guy!