Roon seems an unnecessary extra.
That's fair, but I will add two things to consider:
1) It depends on your digital library and the quality of its tagging
(i.e. metadata). Roon does an amazing job with discovery and indexing a library that, maybe, is not tagged real well. Or is a library that is not supported well with MPD (e.g. AIFF, WAVE or MP3/AAC/FLAC files with which MPD/Manic Moose struggles, like multi-disc albums ... I could go on-and-on, here; many of the issues I've found over the years with Manic Moose have been fixed, and many have not).
2) You like to use room correction and/or DSP functions
, like convolution or pEQ. Personally speaking, I've played around with the open source convolution filters for my collection of headphones - some really sound nice, others I don't care for; think: Sonarworks, but integrated into Roon's DSP processing before being sent to your BDP/DAC (and at zero cost).
I will parrot an earlier comment that at the start of things with Roon, MPD sounded noticeably superior. At some point, Bryston integrated an updated RAAT and that was fixed (IMO). Now, I am not sure I could hear a difference, assuming all Roon DSP is disabled.
As always, YMMV.