Here’s a chart showing the memory consumed by Ymuse.
I’ve reviewed other MPD clients previously, notably ncmpc, ncmpy, and Cantata. The chart includes their memory usage too (all software tested are the latest versions). Note that ncmpc and ncmpy are terminal-based clients. It’s therefore not surprising they are frugal with memory compared to their graphical counterparts.
Ymuse’s memory usage is very respectable. Remember that the figures include the memory usage of the MPD process.