Tough call, and pretty personal based on usage. The vast majority of recreational boaters rarely (if ever) rely on their radar. They avoid inclement weather, darkness, and/or boat in relatively confined areas, or the areas are so crowded that a radar screen lights up like a Jackson Pollock painting. Most boaters rely heavily on their chartplotter and seem to like dual-zoom: close in highway view and a broader scale (I'm not keen on this as the highway view is invariably over-zoomed, but that's a different topic). So devoting MFD real estate to radar may not make sense depending on your boating style. And there are other examples of use-dependent decisions such as fishermen wanting large scale bottom view. Also depends on whether you are running your A/P on a separate control or via your MFD. Same with other monitoring functions such as engine sensors. You can display a LOT of info on an MFD, question is what's valuable to you for your style of boating?
I'm severely limited in MFD real estate. I went with a single screen but would have gone dual if I had room. A/P is a dedicated control head and I added three 4" digital displays. One always shows SOG, one depth, one DTG/XTE nav info. All of these can be displayed in the margin of the MFD, but somehow gets lost or rearranged. I prefer to keep the MFD display as clean as possible. What is displayed on MFD varies depending on what's needed at the time. When anchoring or in shallow waters, forward scan bottom sounder is primary, chart plotter secondary. Standard running on a crowded day, chart plotter at a zoom-out level so I can navigate via visual ATONs. Limited visibility - radar gets center stage, chart plotter second. Docking, wind instrument and maybe rudder angle indicator You get the idea.
I place a high value on the instruments being easily understood by my wife (and crew of aboard), or at least the core information which is why I went with 4" displays dedicated to certain data. Plus they are relatively inexpensive.
Peter