are there upsides/downfalls to single-axle TT's?

Trucking industry has known for decades that as long as 1 tire has the capacity to carry the load, 1 will use less fuel than 2. But for many other factors cause them to stay with duals.
IMHO, if a blowout on trailer causes you to loose control or roll your rig you didn't have control before the blowout. (Fact is the rear axle of TV is where a blowout is most likely to cause loss of control) Just trumping here, but I think there is a better chance with single axle that the driver would notice a issue with all the tires on one side, pull over and stop before the tire beats the snot out of trailer.
Single axle takes less power to turn, because don't need to force axles out of line or slip tires sideways. If fenders are inside body, tandem will use more space.
I buy 1 trailer tire a year, get rid of when 3 YO. But I know a guy that will give me over 50% for my take-offs. His hands feed enough tires to curbs he gets almost new life out of them.

Double axles usually have more cargo capacity. Our Dart has a max of 6k and is 5k or so wet, with a cargo weight of 2k.. Most single axles I’ve seen are under 1k.
Handling should not be a problem if set up correctly.
Tipping over w/ a flat is not a real concern if on relatively flat ground. Limping along w/ a flat might be.
I would think that a 7’ width would eliminate a walk around queen.
Can’t really think of an advantage except maybe cost of tires.

From the owner of a 16 foot Airstream: single axle is one less set of tires, brakes, and axle to replace. Smaller is shorter and shorter is harder to back up. Take that as fact from prior owner of 35 ft mh, 35ft 5th wheel, 25ft Airstream and now the 16ft. Easier to pull and maneuver. Less fuel required to pull. Less expensive tow vehicle to own. No sway in our case. What you have now may well be paid for.

We really like our 16ft. It is what we need now. We recently used it to go to Boston from South Louisiana. Very easy to hitch and go. We just use sway control but no weight distribution bars.

Only had one single axle TT. Loved it...but it was SMALL for 2 of us and crowded for 4. The one item you mention about a flat tire/blowout on single axle is a big safety factor in two axle trailers.

Not knowing your full situation, if it was me, I'd keep the TT you have for (1) size/room/safety, (2) as wanderinggaimlessly said, to do the occasional trip with your teen, (3) for the fact that prices are nuts and might be best to keep what you have.

I guess for me it might make sense to do a 'steady as she goes' approach and do nothing, which is always an option!

When you teen goes off to college, remember, they will likely be coming home in the summers, camping may resume unchanged.
Are you more likely to do longer trips without the child along?
Will your type of camp change from "kid friendly" to more boondocking or touring type of travel?
Instead of downsizing you may want more of a couples touring unit that would still offer a fold out couch for the occasional extra family member.