I am almost 76, my wife will be 77 in October. She is in the early stages of Alzheimer's but still functional and cognitive. We began SS when we were 65. I still work one day a week for spending money and collect dividends from some investments. At this late date is it really worth while to pursue this any further?
The only way to increase your benefit is to work enough to have future earnings that are greater than those in your current high 35 years of past indexed earnings. If you do, then the lower earnings will be replaced by the higher earnings and your retirement benefit will be increased accordingly.
Investment income doesn't affect your Social Security benefits.