If you play games online then a PlayStation Plus is absolutely worth buying - it's literally essential in getting you online and being able to play with pals and teammates. There are also free monthly games: a constantly updated roster of games to download and play that will save you far more than the membership costs each month. On top of that, there are exclusive discounts on the PS Store, cloud storage and save game backups that can really come in handy if you want peace of mind that all your game progress is kept safe should anything happen to your console.
As for the Extra and Premium tiers, well, it entirely depends on how much PlayStation gaming you do and whether the catalog of titles appeals to you. There are some huge PS5 and PS4 games available. Not to mention lots of nostalgia-inducing PS1, PS2, and PS3 classics on the Premium tier like Ape Escape, Syphon Filter, and Resident Evil: Director's Cut. Premium members also get access to game trials for PS5 releases which is a superb way to try before you buy.