Pompeii - possible to just take a quick peak?

Not meaning to be facetious, but there are some benfits to YouTube, drone photography, and 3D imaging. These will give you a better taste than standing at a fence looking in. As it is not fi ished excavating, the fence is some way from the sites, and since a lot was burned, the site is low profile.
There may be some sort of visitor's Centre now, but not when I was there.

I am not really one to insist one does everything available on a trip. But I would drop something else in order to see Pompeii--it is quite extraordinary. That said, if you don't feel the urge, just skipping it would be preferable to driving through the town of Pompei and getting stuck in traffic. Just skirting the site will probably not give you anything you couldn't live without. You'll probably see it better from Mt Vesuvius!

A much shorter walk and a more intense experience for me was visiting Ercolano/Herculaneum between Pompeii and Naples. And you can look down into the excavation better because the relative elevation difference between the surroundings and the level of the town is much greater.

NickB has a good point. I hesitated making the same suggestion. Herculaneum is more intact than Pompeii, particularly on a broad scale. Not having driven it, I am not sure of the feasibility.

Can you, sort of, see a glimpse of Herculaneum without a ticket? Yes, but most of it is in a below-grade pit, so you’ll mainly see the upper half, of some of it. I personally wouldn’t bother. But I didn't bother with Vesuvius either. We went to Pompeii, Herculaneum, and Oplontis, on different days. Loved them. Opinion.

Realize that Pompeii was an entire city when it was destroyed by the eruption, and the size of the excavated area reflects that. As an earlier comment mentions (again, not trying to be facetious), you can see it better on You Tube than you'd be able to do peeking through the fence.

Your horse ride at Vesuvius sounds like a unique experience. I hope you'll come back and tell us how it went!

Pompeii is amazing. We have been to numerous ancient sites and Pompeii ranks at the top for us. We want to return as we were only there three hours.
Personally, I find volcanic landscapes bleak and depressing.

Is it possible to park and just get a quick glimpse of what it’s about
without buying a ticket and walking through the ruins? Sort of walk
the outskirts I guess.

No. If you want to experience the scavi then you'll need to plan time to buy a ticket and go inside. It's a very large and complex site that can't be viewed from the exterior.

For me, an overview of Herculaneum looks like a neatly organized pile of rocks. What is interesting at either sight is walking the ancient streets, going into the buildings, seeing the details of daily life. It's not like the Colosseum or Forum in Roman with majestic visuals. If you want a similar experience and you are spending time in Rome, you can spend 3-4 hours going out to Ostia Antica instead.

I watched this before our trip
It's a good YouTube walking tour - this is just Part 1
https://youtu.be/gaJPcKLyXLQ

Sort of walk the outskirts I guess.

About as worthwhile as driving by Yankee Stadium while game 7 of the World Series is being played inside.

As others have said- no, you can’t just do a quick flyby; especially not without paying to get into the actual park (site). If it were me, at the end of a long jam packed vacation, I would skip it. I would spend that time in a nice Piazza with a carafe of wine and do some serious unwinding and people watching. Might be the best part of the whole trip. 😊😊

Along these lines, has anyone hiked Vesuvius in addition to seeing the ruins, in the same day? Too much walking/exercise?

If your "many sights of Italy" gets you south of Salerno, you CAN get a free glimpse of the Greek temples at Paestum.
We spent hours there.
But, seeing them from the road would be fun. They are large ... and beckoning.

Along these lines, has anyone hiked Vesuvius in addition to seeing the
ruins, in the same day? Too much walking/exercise?

Matt, if you enter "Pompeii, Vesuvius" into the search box and then filter down to forum posts within the last year - to be most current - you'll see that yes, a fair amount of people have done it. Understand that "hiking Vesuvius" almost always means a climb from the transport drop-off point and not from the BASE. That trail surface is very loose so you're going to want sturdy, closed-toe shoes, and some folks report having found it a challenge.

Whether it would be "too much exercise" depends on multiple factors: your fitness level, how much time is spent at the scavi (5 hours for us) and temperatures at Pompeii (heat can take the starch out of you). For couch potatoes and/or with mobility issues, like bad knees, then I'd say definitely too much. It can also depend on where you're coming from and where you need to return at the end of the day. While people do it, I personally would not do both as a day trip from Rome but again, it can depend on multiple factors.

We were fine with just seeing the thing (or what's left of it, anyway) looming ominously over one of the cities it destroyed (Pompeii) and from other locations around the Gulf of Naples when we stayed in that area.