O/O to Small Fleet

I'm an owner-operator, have been for a while, but, with the economy as it is, I personally don't consider adding trucks.
Some segments of the industry are more profitable than others. Swift tried car hauling but backed out of it. I did it for a while, but, the brokers were keeping more than they paid the trucks who had all the expenses and risks.
Some factors;
Driver quality(Vehicle durability)
Rougher roads
Truck Maintenance quality
Road/fuel tax increasing
Truck/trailer purchase cost increased(New and Used)
Government mandated switch to Natural gas coming?

I think unless you have specific local/regional/national freight you can count on in something specific like blanket wrap/liftgate or stepdeck, etc. it might be open to variability wrt return on investments.
You might try a truck and driver leased on to a carrier to see how it goes.
Many customers simply don't know what they're doing and call C. H. Robinson(Zero trucks) or another broker and get late freight or damaged/destroyed freight.
Bidding on load boards is rapidly overtaking $