Hey Corey,
This is a tough crowd so I don't post too much. My father told me something years ago, I am sure you have heard this advise. "keep quiet and let people think you are stupid, instead of speaking and removing all doubt."
With that preamble - I love the old steam gauges in N840AM - (we changed the tail number last year). It is an emotional thing - I like the looks, and I grew up with them. However - technology marches on. I don't need to tell you all the tricks that the G600 MFD can do - it is just amazing, synthetic vision, just being one of so many - but also screen space. I have, like so many people the 750 / 650 combo and in the Commander panel space is a premium. With the MFD's I can put more information up and I don't need to push so many buttons to see it all at the same time. RE Nexrad, weather radar, navlog data for my waypoints coming up, distance, time eta, time ete, etc. I love having every piece of information available at the same time at a glance.
Let me digress a minute. Years ago we had a C414 with the standard Cessna avionics. I remember when my Dad (we all flew the airplane) wanted to get a Northstar M1 Loran. I remember (being a young business school graduate) thinking "what a waste of money". How much faster will we get to our destination. How much money will that little black box save? I thought 2 minutes, 5 minutes. Why bother. My Dad didn't listen, he bought the M1 and had it installed. We all LOVED it! After we flew with it a while - we thought "how could we ever go back?" In my OLD OLD OLD AGE, I have come to see this technology as an never ending avalanche of improvement. An extremely expensive avalanche. But of all the things I get to do in this life - flying is one of the most fun, and flying my 840 is one of the most fun airplanes I have ever flown. The G600 is just plain cool and fun!
Now let me say a few more things. We have a Cessna 210 that my sons fly. It happened to have a 750 / 650 G500 panel when we bought it. It didn't seem right that the 210 have a better panel than the Commander - right? On a more serious note - I do believe having some systems commonality in the panel makes some safety sense. Right?
And now in my final argument. The GPSS steer has never worked in N840AM. Not that I "neeeeeed" it. But I like stuff to work, and the 210 does the coolest GPS approaches with the autopilot. (I am guessing that is what Don is getting, by the way. Rumor has it that he is the launch customer for the Genesys 3100 autopilot. Am I allowed to guess that on line?). So any way, There is a data port on the old DG that is supposed to send heading information out to the rest of the avionics. That data port, or cabling does not work. So a lot of stuff in the airplane doesn't work just right with the 750 / 650. Sooooooooo, I do have some "broken" stuff in the airplane - and it only makes sense to upgrade to the G600txi.
Okay okay, my final final statement. What else are you going to do with the money? If you can get your wife and partner to go along with it - upgrade. You won't be sorry.