Convert Oscillator output voltage level
No one has "infinite input impedance", and everything has "intrinsic capacitance and inductance associated". The question is how much these parasitic parameters would affect the signal. All you need is to have a signal strong enough to toggle the input buffer of XTAL circuitry near 1.8V/2 input threshold, or 900 mV +- 200 mV, that's it. 

If you want to reduce a 3.3 V signal coming externally from an oscillator over transmission line (PCB trace), just terminating the signal with characteristic impedance (say, typical trace of 60 - 65 Ohms) at XI point will instantly halve the voltage, without any divider. The transmission line will be that divider, especially if you match the transmission line impedance at input side using some reasonable series resistor (22 - 33 Ohms, at oscillator end). There will be no reflections or any other ugliness to worry about. 

So, the short answer is that all these "intrinsics" are totally negligible at 24 MHz or even ant much higher frequencies. Your worries are absolutely unfounded.