Is this for gaming? If so, you probably won't need more than 16GB any time soon, as only a limited number of current games are beginning to nudge over 8GB of RAM usage. I would expect 16GB of RAM to be enough for running any game at ultra settings for the next few years or so. Any unused RAM will just be sitting there, not doing anything.
Unless you know that you need more than 16GB of RAM for some specific task (like certain video editing software), I wouldn't bother, and would upgrade other components instead, especially since RAM is still priced relatively high right now.