These wacky holidays may be cheesy, but I always look forward to National Best Friends Day in particular because it is a specific moment for me to take time to acknowledge the relationships that have been so special in my life. It might be a phone call or a card, but those small gestures mean a lot to their recipients.
Oh, so you celebrated that friend as your best friend... I see. Having a day where you celebrate a best friend can lead to people feeling left-out. How would you feel if you picked someone who in turn picked someone else? In addition, if you make a national day out of everything, it will cheapen the whole idea of the national day.
I don't really think it is important to celebrate a best friend. It is enough that a person hangs out with their best friend, spends time with them and lets them know they are appreciated in the other person's life. Celebrating a person would serve no other purpose that can't be accomplished by just telling them how happy you are to have them as a friend.
No, National Best Friends Day should not be celebrated as it is not a real holiday. This is similar to National siblings day, in that these are made up days to celebrate people who should be celebrated on a daily basis as they are very important in your life. It is not necessary to make a specific day for them because they are already a hugely important and thus appreciated aspect of your life.