what kind of problems can I expect with purchasing a kingpin w/ 3o,ooo miles on it?

No troubles as the bikes are pretty much bullet proof.

Maintenance issues are always the problem when buying used.
Check that services have been performed. 30,000 is the first BIG service to your bike.

This is a list of the 30,000 mile service replacement recommendations
Drive Belt, Brake Fluid, Oil and Filter, front fork oil, Spark Plugs

Lubrication Service items at 30,000 are
Clutch, Fast Idle, Front Brake Lever, Control Cables, Gear shift pedal, Rear Brake Pedal, Steering Head Bearings, Sidestand, Throttle

I bought a 2004 KP with 28,000 miles, albeit from a dealer here in Minnesota, and it was terrific. No problems, and rode it another 6000 miles before trading it for a 2007 KP Tour.

Victory engines are superbly engineered and assuming its had regular maintenance, you can rest assured that the bike will perform as well as ever. There are many, many Victory motorcycles with over 100K miles, still on the road with grinning riders.

Go for it.