Whether you can eat potato salad or not is asking for personal medical advice, which we can't provide. You should check with your doctor to be sure. However, potato salad is almost all carbs just like rice and pasta, so your doctor will almost certainly say no.
Yes, high glucose is dangerous if it becomes chronic. Consider this:
Almost any part of your body can be harmed by too much sugar. Damaged
blood vessels cause problems such as:
Kidney disease or kidney failure, requiring dialysis
Vision loss or blindness
Weakened immune system, with a greater risk of infections
Nerve damage, also called neuropathy, that causes tingling, pain, or less sensation in your feet, legs, and hands
Poor circulation to the legs and feet
Slow wound-healing and the potential for amputation in rare cases
Your glucose level is barely high at this point, so that's why your doctor recommended diet modification instead of medications. If you follow their advice, you won't have high blood sugar and won't suffer the consequences listed above.
If you want your rice, pasta and potato salad in the future, the best way to get them back is by reducing your blood sugar levels, and the best way to do that is by losing weight and exercising more. It really will make a difference and probably allow you to have potato salad again in the future.