Funnily enough, I've just started a process of going through a lot of the paperwork I've generated from old campaigns, including a lot of stuff I hand-wrote when I was a teen. It's being scanned and stored electronically, and then the hard-copies disposed of to make room. But looking at all that stuff has been a bit of an eye-opener!
I think possibly the biggest shock has been the sheer amount of time, and the number of pages, I've wasted on trying to find exactly the right set of house rules for the game - even going so far, on more than one occasion, as trying to rewrite the entire game from scratch to better suit. Invariably, each attempt got a certain distance in before I either got bored or drifted off, or had a better idea part way through that necessitated huge rewrites.
The one time I did complete one of these projects, I almost immediately decided I didn't really care for the result and promptly went back to the real game.
Then again, I'm not convinced that counts as an improvement - the main thing that stops me from trying to massively house-rule 5e is a lack of time.
After I got back into gaming after more than two decades away from it, an old friend of mine who remained very active in the hobby sent me a binder of campaign stuff from high school. A few things stood out:
1. My handwriting has not improved.
2. My writing was pretty good back then. I'm not sure that I've really improved that much in this regard, mostly because my writing has been almost 100% non-fiction business-related writing.
3. My map-drawing is decidedly worse. I rely on computers now and am hopeless with pencil and graph paper.
4. Boy did I like my details back then and I sure loved lists in the days of 1e. I mean, I have an inventory of books and their prices for a bookseller in one of my cities. Now, I like me random lists.
5. Related to 4. I am much better at making things up on the fly. E.g. no way am I going to have an inventory of books. I do have some random lists, but I'm also much better at just making up a title. I think this is partly because of necessity, I don't have the time for prep and world-building that I did in high school. Also, I've read a heck of a lot of books in the past couple of decades. I also read all the books in Skyrim. I just have some title patterns in my head and it is not difficult to fill in the blanks to come up with a book title on the fly. Similar situation with tavern names and menus. Also with NPC names. I've traveled a lot and lived in multiple countries since high school. It helps me make up names on the fly. I only use random lists when prepping games, but during play, if I have a non-prepped NPC, I can usually come up with an appropriate name. But in the 80s it was lists, lists, and more lists.
6. I played with a lot more female gamers in the 80s than today. My monthly game is pretty much guys game night. Not saying its good or bad, just interesting given the stereotypes and trends in the hobby.
7. Characters feel more special when you wrote down everything in pencil because photocopying the formatted sheets in the back of the books cost money and never had enough room to write everything, especially when your penmanship was terrible. You literally created your character from a blank page. Making it feel disposable at low levels and unmeasurably precious at high levels. There is this stereotype of a DM ripping a character sheet in half at death. For players today, in the era of digital character sheets, that's just funny showmanship, but in the 80s it was heartbreaking and/or enraging.
8. Holy moly did I know my office supplies. I don't even know where to find some of the tabs and book-corner protectors, I used back in the day.
9. Every gamer was an artist in the 80s. Not a good one mind you, but looking at old notes and character sheets, everyone embellished them with marginalia art, character portraits, family crests, fantasy religious symbols, etc. Now we search Deviant Art or do a Google Image search and cut and paste it into our digital character sheet.
10. I and my fellow players apparently have much better table manners. Boy are my old materials stained with all manner of mysterious liquids and greases. I don't even have finger smudges on my 5e stuff. My mom would be proud.