Input impedance can't be determined simply by looking at the tail resistance. To gauge input impedance, first thing to look at is input bias current.
You can get a crude idea by setting 0V DC as your incoming signal. Measure input current. (It's easiest if your system yields 0v output when fed 0v input.)
What to use as the voltage differential? Tentatively, the negative supply rail. Because input signal current generally takes the path down the emitter leg and tail resistance (assuming we're talking about NPN transistors).