Is there any collectible value to Japanese N-scale steam engines, or did I get upsold?

You probably did better than you think, and the shop guy almost certainly knew exactly what he was doing. From your description those all sound like Kato products, and stores around the big stations in the Kansai area often carry shop-exclusive or limited versions that ordinary retailers never see.

The bigger loco with the tender is almost certainly a C62, the most famous Japanese express passenger steam engine. The one that matters is C62 2, the preserved running example at the Kyoto Railway Museum, and some releases of that specific road number were only sold through select shops. Flip the box and check whether it names an actual road number rather than just the model, and look for the two kanji characters that mean limited, or the words Limited Edition in English. If those are there, hold onto it. The bird emblem is a nice clue. My guess is a swallow, because the C62 hauled the Tsubame express and Tsubame literally means swallow. If the emblem appears on the loco box, that points to a Tsubame-themed edition, which collectors pay extra for.

The small black engine with the gold-trimmed coaches sounds like one of the compact starter sets, and the single brown coach is likely a replica of a preserved historic carriage, the kind of thing the Kyoto Railway Museum sells as shop-exclusive stock since it sits right near there. That would explain the whole haul: the guy was steering you toward museum-linked and limited pieces, not tourist bait. For dating, the box bottom tells you most of what you need. Kato prints a catalog number and a copyright year, and the maker name is always in roman letters. Tomix and Micro Ace do the same. Anything from the last decade or so is a current-tooling model, and limited editions from recent years hold value well. As for sealed versus running: Japanese N rolls on the same 9mm track as any other N scale, so nothing is exotic there. Since you are an HO guy, I would keep them sealed and stored somewhere dry and out of sunlight. Limited Japanese steam sells quickly on the collector market if you decide to let them go.

Following this becuase I did almost the same thing at a hobby stall in Tokyo last year, bought a little boxed train set mostly by pointing and smiling. Mine had a sticker on the plastic instead of anything printed on the box, wich confused me when I tried to look it up later. One thing I noticed is the Japanese writing on my boxes has a bunch of small numbers mixed in with the characters, not sure which of those matter. Do you have a friend or coworker who reads any Japanese? Mine just snapped a photo of the box with her phone and the translate app sorted it out in seconds.

Back in the late 80s the only way to ID something like this was to photocopy the box art and mail it off to an importer, then wait six weeks for a reply. Kids these days just point a phone camera at it and get an answer in seconds. Anyway, one thing I'd add: before deciding sealed versus run, put your ear to the box and shake gently. If you hear anything sliding around loose, the foam or blister may have shifted in transit and you want to open it and check for broken details before that matters to the value. Learned that one the hard way after a move cracked a handrail on something I'd been sitting on for years. Any model railroad club near you will have an N scale loop you can test them on without buying track.

I picked up a Japanese steam loco on a work trip a few years back and faced the same sealed vs run question. What I ended up doing was giving it a slow lap on a spare piece of track every couple of months. Motors that sit untouched for years can get stiff, and mine ran noticeably smoother after the second short session than it did out of the box. Doesn't have to be a whole layout, just a straight piece of track and a simple power supply. If you do sell later, running it once or twice won't hurt the value, and you'll know the thing actually works instead of guessing. Also grab a translation app for those box photos, it sorts out the kanji fast.

I'd take the 'hold onto it, limited editions hold value' line with a grain of salt. I bought what a shop in Nagoya swore was a limited run about eight years back, kept it sealed, and when I finally checked sold listings it was basicly fetching retail. Turned out the 'limited' kanji on the box just meant it was a shop exclusive for that store, and Kato had reissued the same loco twice since anyway. thier popular steam models get rerun every few years, so sealed only means something if that exact road number stays out of production. Check the catalog number against completed auctions before you decide it's a retirement fund.