Is it wise to use analog input pins to read digital buttons?
The Analog pins are essentially identical in functionality to digital pins when used as digital I/O.

If desired you could "be clever" and use an analog input in analog mode to read multiple keys using one pin. eg using 10k, 22k, 39k, 82k, 150k in series with 5 buttons from V+ to pin and a say 4k7 to ground would result in 5 voltages which were easily distinguished using an analog read. This is a very very old technique indeed and allows far more than 5 keys on one input pin. THere are limitations which can be discussed if required. 

R1 ... R5 correspond to buttons 1...5

Vout = V+ x Rb / (Rb + Rbutton)

Example only  

Rb = 39k
R1 = 10k
R2 = 22k
R3 = 39k
R4 = 82k
R5 = 150k

Gives   


The % of V+ in column 2 when a button is pressed.  
The voltage in column 3 with V+ = 5V 


Delta-V is the difference between that key and the one below - very ample clearance.