I have a modern race bike, less than 3y old with some but not all of the latest aero features. I also still own my 30y old racing bike that I used to race until 20years ago (it was already old bike then). It stays at my parents place and I ride it maybe twice a year. If you ask any bike reviewer he will tell that old bike is obsolete, feel much slower and make me lose 45s over the course of a 50km ride according to the data given by the manufacturer. If you ask me, sure I feel a difference, mostly in feeling, when I start riding the bike. But after 5 minutes all this is forgotten and I enjoy the ride as much as on my more modern bike. And that bike is perfectly fine surrounded by superbikes in a group ride. Actually I did one this summer with a group that tend to stay together but ride at a fast steady pace until the last 20k where the wait "policy" disappear and people start to attack the climbs at max pace. I ended up in the 5 rider leading group out of maybe 40 and I was totally out of shape.
That old bike would sell for 300-400€ in the second hand market right now. The difference with a 2k and 8k modern bike is much lower.
