Considering a POSSIBLE replacement for speakers. Opinions?

At that price point, it's a no-brainer to go with the Linkwitz LX521.   Not even close.  Mind you, it's a DIY project that will take some research on your part to learn about them and the amplification choices, but this is a loudspeaker system that does NOT require a sub-woofer and images exceptionally well.  It takes you into the land of open baffle loudspeakers, tri-amplification and DSP EQ.  They compare well to the big MBL loudspeakers which retail at $70,000+.

Do your homework.   You won't find them on the used market.   People build them and love them.  This would be the very last loudspeaker you would ever purchase.  Read about them at The Linkwitz Lab website.

If you're not brave enough to do that, then seriously consider the SEAS Thor kit from Madisound.    The bare kit costs $2231.40.  Madisound has a cabinet maker they work with who will build them and have them shipped to your door for about $1000 more if you're not brave enough to build them yourself.   There is a used pair on US Audio Mart. 

This is a design that is extremely similar to the Joseph Audio Perspective 2 Graphene, which retails for $13,000.   Both are transmission line enclosures which used SEAS Excel drivers.

Find some used dynaudios - I'm currently in love with my special 40's.

As someone else wrote, the Monitor Audio Silver 300's are the new model version of yours, if you like Monitor Audio Speakers. I have a pair of Silver 500's and I really like them .They are the same speakers but with 8" woofers instead of 6". For some people the 500's might have too much bass and they prefer the 300's.

Call Coincident Speaker Technology . He has introductory floor model speakers at a reasonable price . My friend bought them and they sound good . It's not one of the ones pictured on the website , all of which are more expensive .

I'm in similar boat as OP.  I have MA Silver 6's and have really enjoyed them again since i've optimized much of my system around them.  I have enjoyed listening to other speakers but am wondering how much I'd need to spend to get a quantum leap in performance.  
@stereoisomer  I think making a leap across family to MA gold and the ribbon tweeter might be the biggest bang for the buck leap you can make.  Never mind the finishes on the gold line are simply gorgeous.  I'm not convinced moves within the silver line, or moves to a different manufacturer at a similar price point, would buy you a ton but will monitor this thread for real world experiences.   Good luck!