On a $30 lawn $10 extra a month I'd be losing money. Then have you figured in the cost and markup on fert, lime, weed and feed?
It is one thing to be in business long enough to only have full service customers.
Most customers only want edge mow blow.
Then is that $10 going to also cover hedge, shrub, and tree pruning, and while I am at it weeding in addition to the other things that you mentioned as full service?
I will provide the level of service the customer wants. I don't low ball. Just mow is ok. What is important is not how many hours I can bill one customer. That I have 40 hrs of billable labor every week.