If I was getting 30 calls a day this is what I'd do....
Buy a couple used S10's, put your logo on the side. The S10's wont eat tons of gas and can still haul a small trailer/mower just fine. Find a couple small 6x10 or 6x12 trailers, purchase another hydro 36" and a couple push mowers. Hire a couple guys at $9-10/hour.
I don't see any reason each guy shouldn't be able to do 12 lawns a day by himself.
So for example now you have 3 trucks out mowing 12 lawns each day Mon-Fri.
3 trucks x 12 lawns = 36 lawns per day
36 lawns x $25 = $900.00 per day gross income
Wages: 2 employees x $10 an hour x 8 Hours = $160 per day.
Gas/Misc Expenses: $200.00 per day (strictly a safe guess, but much more than you say you spend a day.)
Your daily estimated operating costs are around $360 per day and you gross $900.00 per day give or take. This leaves you with a net profit of around [B]$540.00 per day.[B]
You could even hire a 3rd worker to run your truck, sit at home and watch the price is right and still pocket over $400 a day.
I realize there are other numbers/costs and variables, insurance, etc.. to figure in, this is just an example of another way to think about making your business more productive and profitable since acquiring accounts doesn't seem like an issue.