Hi, I think the Agenda is still absolutely relevant! I have an LV PM, and I use it for private events, highlights and thoughts. It feels good to write things down. I don't carry it around, because I want to preserve its condition and I don't want people to see my LV agenda. It stays at home on my desk, and I check it out on mornings and evenings.
At work I use a medium-sized agenda, such as those from Moleskine. As a back-up for everything, I also use the calendar on my iPhone and iPad a lot too. It is always with me and it notifies me about meetings and appointments.
For my PM agenda, I like to buy refills from LV. They are pricey, but definitely look cute and they come with stickers. At the end of each year, I keep "relevant" pages and add them to the new refill set. My "relevant" pages are those with memories or major events that make me smile on sad days. Hope this gives you good input to get an agenda!