If you want to play 5e, you are going to need the 5e core books. Unless you want to spend a whole lot of time and energy converting old monsters to 5e, you will need to buy the 5e monster books. Unless you want to spend a lot of time and effort converting old classes, prestige classes, magic items, spells, etc. to 5e, you will need to buy those 5e books as well. That's a lot of 5e books to buy, and take on new settings and adventures if you want any of those.
Unless of course you don't want to play 5e. Then you can ignore 5e releases, but are also not in the demographic(5e players) being discussed in this thread.