A bit late now, but years ago I would have gone to two dollars. A price increase to two dollars now, even with an increase in time will look like you have doubled your price. Obviously you want to increase by a dollar as you want to stick with the dollar
coin platform. When I opened 7 years ago, I was at $2 for 4 minutes. I was then at the high end for my area, but I have always believed in washing fewer cars at a higher profit. My wash functions always work, and I am very quick with customer response on issues. I have recent gone to $3 for 4 minutes. So....getting back to your question, since making the price change I have noticed a nice increase in average spend per
transaction. Most customer feedback has been that of a positive and understanding nature. I did have one customer demand the 50 cents back he had deposited prior to seeing the start price. Quite frankly I am happy not to have home as a customer. In your case, I would increase to $2 ASAP, even if you choose to increase the time to 4 min, as you likely will see an increase in spend and a decrease in cheap folks leaving a mess after spending a buck.