Is renting a server worth it?

It depends on a couple things.
Game mode
Experience
Player Slots

The game mode you choose is one thing. You have to like the game mode you choose or you will get board and just be wasting money on a unused server.

Your experience is also something pretty important. If you don't know what your doing or don't have the patience to figure it out it's not worth it.

Depending on your game mode your recommended player slots will differ. If your doing a party game mode like Prop Hunt, Deathrun ETC, you should only need about 15-25 slots. If your doing an RP like Darkrp recommended would be 40-50 slots. If your doing like a MilitaryRp or PoliceRp I would recommend 60-80 slots as you probably should use a fairly large map.