Valkyrie no Densetsu (1989) was eight years old when it was released on Namco Museum Vol. 5. The original Namco Museum Playstation game is eleven years old. In other words, Namco Museum is now older, in relative terms, than a game that was old enough for Namco Museum.
Speaking of the Playstation editions, the new Namco Museum DS has something not seen since those days: an actual museum mode, in the form of a trophy collection and music player, as well as scanned instructions and flyers.
Relatively newer features include bottom-screen maps and hints for Galaga (?), Xevious, and The Tower of Druaga. Of course, the most exciting relatively-new thing is Pac-Man Vs., which, now that it won't require so much of a financial outlay, we may actually try with another person.