I do the same thing you do....just touch them up between trims.
There is some geometry involved and knowing what a horse needs in the way of angles etc.
As long as I can afford it, I'll let the pro take care of the major part.
That said, Obama is president and who knows how long we'll be able to afford the farrier.....
For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.