+24V supply versus +/- 12V supply
It will matter only if you have a connection that uses the "ground" at 0V in a +/-12V system. If you have only connections that use the +/-12V rails but never touch the 0V ground then yes you can a 0 to 24V power supply. Obviously, if you have a line that uses 0V in a +/-12V system you could substitute that with a 12V line in a 0-24V system. As you said, voltage is just a reference. It's all about the difference.