Based on the adult PC game by Orc Soft.

Anime: how can I enjoy old anime when I have been ruined by the better art styles of newer anime?

It is the other way around - usually older anime has better, more detailed art style, while newer one is streamlined and overly clean with a lot of glow/bloom going on in it. To transition to older art style, start watching movies with higher budget. For example, Patlabor movies directed by Oshii and “early days” ova: Original Ghost in the Shell (the first movie), Akira, Gunbuster: Outlaw Star: Slayers series, something like “Twelve Kingdoms”, Utena and the like. Big O is worth checking out as well, despite unusual art style: And then there’s Tenchi Miyouh: And Miyazaki’s works, Trigun: And others. As long as you stick with higher budget movies/series, ovas and full-length movies, you’re going to find a lot of highly-detailed art.
This will allow you eventually to get used to older, “softer” look of anime.