Is WOW worth getting back into? I quit after the Pandaria season. I had many thousands of hours but I just ended up getting bored unfortunately. Genuinely not sure if I want to buy all those DLC to catch up. Is it worth doing?

You dont have to buy each DLC anymore. Usually you just need to purchase the latest and you are set, so the cost isnt that bad to get started in term so $ having to be spent.
I personally havent touched retail for a long time, but i return to play classic every now and then which is lit

I came back there and, between the latest expansion - I was peak active during MoP too.

What I find hard is the commitment and the speed at which it changes.

Like Dutdut said, you only buy the last expansion and you'll be good - but keeping up with all the changes + the grind is extremely difficult and hard to dive back into. By the time you find your way back into it, it seems they release another pack.