Current limiting resistors are not strictly needed on inputs, because inputs do not draw any current from the voltage source that you hook up to them (well...just a wee bit of current, maybe a microamp at most).
When the potentiometer is all the way at 5V there is no over-current, because it is the pin that *draws* the current from the 5V; the 5V does not force any amount of current. If the Arduino pin requires only 1uA of current, then only 1uA of current flows from the 5V source.
You would use a resistor when setting a pin as an output because you do not know how much current will be demanded by whatever you hook up to it. In the worst case, consider hooking up a plain wire from the output pin to GND (0V). That would allow an infinite (theoretically) amount of current, blowing up the Arduino. The resistor limits this to 5V/R (slightly less, since the 5V output pin voltage decays as more current is drawn from it).
Now, if you want a degree of protection for your Arduino input pins you WOULD connect a series resistor, in the case of overvoltage (>5V) or undervoltage (<0V) because in those cases the Arduino input pin will draw a LOT more than 1uA, and this can damage the pin. So it's not a bad idea if you have the space and patience to add resistors. A 1k resistor would be suitable for a 5V source as it would limit current to 5mA or so if the source went >5V.
It would not make a difference if you used a 30k potentiometer. As you say, when the pot is throttled all the way up you would still be applying 5V directly to the pin through no resistance.
: compatible with Arduino UNO, 24V operation, all I/O's fused and protected