I have Silver Medallion status through ‘25. I don’t always fly on Delta, but I could arrange it so that I hit Gold. The big question…is Gold really that much better than Silver? My primary interest would be automatic seat upgrades.

It entirely depends on your travel patterns, but you are more likely to receive upgrades as a Gold than as a Silver. On many routes, though, neither are likely to have upgrades to first class clear.

There are other differences in benefits that are most useful for international travel on skyteam partners.

Priority pass

Separate line at security.
priority baggage handling
earlier boarding?

Realistically, the only thing Silver gets you is a free bag. Gold gets you skypriority benefits at the airport and for boarding, and also T-3 day upgrades vs T-1 (which are relatively useless).
With T-3 you'd have a decent shot at C+ seats depending on the route, and occasionally a first upgrade. But, if you're not going to fly DL much next year to enjoy the benefits then don't bother.
Also if you are located at a major hub like ATL/MSP etc then its not going to be much of a difference due to the large higher level elite presence.

Free Same Day Confirmed changes is nice.

My kids under 18 can’t get an Amex. I travel with them frequently on separate PNRs with work paying for my revenue ticket and I use miles for them. The huge advantage of giving them Silver Medallion status as my PM choice benefit is the better (blue) MC seating they can get on their own PNR.

We live in a small community with direct flights to SEA and SLC only. There isn't a lot of demand for comfort plus and first class on those routes though. We've been upgraded one or two classes multiple times with silver. I need to go to Japan. If I choose Delta, I'd bump to gold, but accumulating miles on another carrier would probably serve us better. Just trying to decide which way to go.

Non-US Skyteam Lounge access (+ 1 guest) on international Skyteam flights is a great benefit of Gold

Priority Pass is a real thing that isn't Delta related.

I'm assuming you're talking SkyPriority, which is nice to have. But if you're flying domestically to random outstations, it's not of much help. There's no priority security lane at most airports, thinking GNV, SDF, OMA, etc. At ATL, JFK, SEA, yes, but otherwise no. Baggage, meh. Boarding, meh.

FWIW, if you have a Delta Amex, they can get one as an authorized user as young as 13.

There is a handy comparison chart on the Delta website.

Golds are not a ton better for upgrades than Silver (which tend to get upgraded only on weird outlier flights).

If you're flying Main, it's nice to get priority seats (if available) for free and slightly nicer to board in whatever they've replaced "sky priority" group with--at any rate, in advance of "lower-status" Main passengers. (Nothing against them but I do think the PMs/DMs who will be in Main ahead of you tend to be more experienced fliers with more familiarity with the Delta setup, meaning less waiting in the aisle for someone else to figure out how an overhead bin works.)

Gold gets you lounge access when flying in F to/from Canada--an obscure perk, to be sure, but one that happens to sometimes fit my personal flying patterns.

(That said, I'm bidding fair to drop from Gold to Silver this year and I can't see making extraordinary efforts to keep it.)

Correct. But even if I spend $1M on it they can’t earn Silver or Gold status to get good MC seats unless I gift it to them.

My (admittedly very crude) schema to explain it to others is this:
-Silver is good for exit row seats and Comfort+ maybe 30-50% of the time and the chance First upgrade (maybe once per year)
-Gold is good for fairly reliable Comfort+ upgrades and off-chance First upgrades (say, on a fairly an empty flight).
-Platinum is good for instant C+ upgrades, somewhat decent First upgrades (especially on not so competitive routes) and RUCs.
-Diamond is good for instant C+ upgrades, Zone 2 boarding, and better First upgrades and RUC/GUCs.

Yes, the upgrades are very route and timing dependent, so don't throw tomatoes at me for this crude characterization!

If you have a choice--and especially if you're booking using OPM and Delta flights don't cause you to have to take a connection (over direct flight with another carrier), I'd go for Gold for more reliable C+ upgrades and SkyPriority access (the latter being most relevant if you're at a hub and might check bags; at most outstations, SkyPriority line includes Silver Medallions).