is purchasing gold/diamond worth it ?


Depends on the amount of time you have to use the lessons and drills. Not enough time to spend 4 hours or more a day learning from the lessons, practicing the drills, playing and reviewing your own games against people and computer on a slow enough time control to think, then no. If you have enough time then yes.

If you’re talking about the free trial, sure it’s a free trial why not. If you’re talking about paying for the diamond membership then as mentioned above, it’s worth it if you have time to utilize the features it provides- otherwise no.

I heard a dozen of stories from people I work with who took the free diamond trial, forgot to cancel the free subscription and then became paying members, and didn't use any feature.
If you're interested in trainings, I would rather suggest a good old book (Nimzovitch, Euwe, Alekhine, Pachman...) or Chessbase trainings.
If you're interested in the analytics, then why not...
To me, most of the features offered by the diamond status are cold numbers. Maybe I'm wrong, I didn't try diamond from the various reports I had.

Depends what $100 is worth to ya. There's people who could really use that money, and there's people who can spend it without noticing.
I like to have the various services available when I want them, even if I don't use them all that much. I wouldn't say it's essential, but I like it.

Honestly, use lichess for puzzles, game reviews, and spend some of that 100 on good quality chess books.