Is that retro Pioneer single-DIN actually any different inside, or is it just the looks?

Short answer: it's the same guts. Under that retro face it's basically their current top single-DIN with a fresh skin. Same amp section, same Bluetooth, same tuning, just wrapped in the old-school display and that chunky knob. So yeah, the people telling you it's a nostalgia tax are right. You're paying a big premium for the styling and nothing else.

Yeah that reply lines up with what I found when I messed with one at a shop last month. Guy let me pull it off the demo board and plug my phone in, and everythign felt identical to the regular deck they had next to it, same menus, same lag scrolling through sources. Only real difference was the look. The flip door on the demo unit already had some play in the hinge from people fiddling with it all day, so I'd guess that cover is the weak spot like you figured. If the internals are the same anyway I'd take the cheaper one and put the savings into speakers like you said.

That's a shame about the hinge on the demo one. I was wondering the same thing about the little door since my last deck had one of those flaps and it got looser every month til it just hung there. Kinda pushing me toward just keeping my plain one anyway. Does the orange screen have a dimmer for night driving? My old one glowed like a night light and it bugged me on long drives.

I went through the same debate last year with a different retro-style deck and ended up buying the pretty one. No regrets, because I look at that thing every single day and the plain slab I had before bugged me every time I got in. Install was painless too, the thing that saved me was a plastic trim pry bar, popped the dash clips without leaving a single mark. Cost a few bucks and I've used it three times since. If the styling is what you're actually after, the speakers can wait.