I made it just in time. Only had the value for 2 extra skill points sadly. Need to learn better loot routes or play more to get them all probably. Looking forward to getting to be afraid of arc again.

I did it the first time, it made me stop playing. I felt accomplished and I didn't want to redo the quest all over again

Didn't even try. Did it the first time but skill points on a tree full of skills that really don't make a lot of difference to the game IMO is a shitty "reward" for how much work you have to put in to do some of the requirements.

Since the last expedition my play time dropped off drastically anyway because I really don't feel any incentive to keep coming back to the game without any kind of goal to drive me along.

Yup, and I also did the catch up too. I got Equaliser blueprint early on this time, which makes money farming easier. Game's so much fun when you realise you can just buy Anvils off of Tian Wen.

can someone explain to me the point of doing the expeditions? the only thing i understnd is you lose almost all your progress...

Starting off fresh so that you get that early-game feel again, whilst also collecting some minor benefits. Bragging rights too, I guess.

Everywhere I read about it, people kept saying it's not worth it. I just did it - I'll see.

In the patch notes it should say that somewhere, but the rewards seem helpful (apart from the fact that you can start the grind over):
You get more total skill points to distribute, more storage space, faster leveling and more resources from scrappy.

The difference isn't crazy, so maybe that's the reason, but I did it anyway. Mind you, I never had any looting route in mind, just went for the area where there were more trinkets (Buried city seems somewhat okay for that), picked up stuff that I wouldn't normally, but it sells decently (even arc performance steel, drivers, hell, even full stacks of arc alloy), and tried to craft whatever I could, instead of buying it.

I read somewhere that the amount required was decreased from 5 million coins to 3 million for the maximum reward because it was way too grindy. I went for 3 and ended up with ~5.3 by yesterday, but I have no life.

Not this time, not the first one either, probably the next one? I'm still not done collecting blueprints, finishing quests, etc

I skipped this expedition. I still think it's not worth it to wipe all your blueprints and crafting every two months for such small rewards.

Skill points are quite insignificant. Blueprints are not.