The Monarch 7 is a VERY competent mid-level binocular. Nikon Monarchs have been reliable <$500 options for literally decades, and the M7 finally addressed the biggest flaw which was the persistently below-average FOV's. Throw in compact size, pleasant ergonomics, light weight, that predictably smooth Nikon focus knob, and bright modern coatings and it adds up to a very nice package. Sure, they don't have great edge sharpness or perfect CA control, but if you get the bird in the middle of the view it's 90% as bright and sharp as anything really.
I had the M7 8x30 for years (wife bin) until she upgraded to the Ultravid HD 8x32 earlier this year. I compared them pretty carefully before selling the M7's, and honestly if you just pick them up and look at stuff, just use them vs. inspecting the optics, the M7's were at least ~90% as good as the UV HD in terms of brightness / contrast / color / clarity on axis.
To put it another way: the different between a junker $50-100 binocular and the Monarch 7 (or any other top $400-500 binocular) is orders of magnitude greater than the difference between those $500 binoculars and the top dogs.
A good sample of a Monarch 7 is approaching 90th percentile of brightness and usable sharpness in the sweet spot for handheld field use. The only significant optical flaw (given the price point) is the glare problems, which seem to be worse in the 30mm models (ruined the 8x30's for my wife and I). Not everyone sees glare equally though, my wife is WAY more sensitive to the veiling glare than I am.
So, since everyone seems to be nodding along with the "keep the M7" advice...... I'll throw you a curveball instead: rather than taking a loss on the Monarch 7 doing the flip to a better Monarch in the same format, why not get something totally different to complement the 10x42's? I'll bring up again the Kowa Genesis 33 sale for $799 right now, ending soon. The Genesis 8x33 are spectacular (unless you're an edge peeper, and if you like the M7 then you probably aren't) and would add a new format to the stable. $800 is close enough to the gap between $200 profit selling the M7 and buying the MHG right?
I wouldn't be surprised if you get more usable sharpness in the field with the lower mag Genesis than you do with the 10x Monarch 7's as they are amazingly sharp and bright but have a wider, deeper FOV and will be steadier to hold. You may love them so much that they replace the M7's as your primary field optic and the M7's can be the backup option or for dedicated 10x usage for longer distance viewing.