Iirc needs are supposed to be up to ±50% speed and skill - not sure if before Legendary+5 cap or after it, and even then Accomplished is still pretty good. I also notice Distracted! forgotten beasts don't react as well, maybe not move as well either?
Ultimately, perhaps the biggest reason to fulfil needs might be that the blinking downwards yellow arrow is annoying. It's also something to do.
Fulfilling all needs of some dwarves should be possible, though at the same time is more difficult. If you take the temple-reciting quite focused Meng above, all his missing needs can be fulfilled. You'd need a herring to eat, a masterwork trifle pewter amulet to haul and acquire, an excellent pair of socks to wear, a book on the construction of windlass to learn, a spouse to speak with, a plant to gather and a sword to kill weak wildlife with.
You'd also need to do this all before the other needs degrade to normal levels. I'm not sure what the decay rate is (from max 400) and how need_level affects it, counting 100 steps only has degradation by 1 for drinking alcohol or acquiring something.
Heh - and you'd need to decide to do all this instead of ordering Meng to produce an extra item or two.
For making new friends, one player has reported some success with multiple smaller places to meet, making it more likely for dwarves to spend time adjacent to each other. Though obviously, nothing beats prenuptial paired suites for getting them to marry, which is my recommendation - don't brother with larger meeting areas if this is your goal, just lock them together in a cramped room with food and drink. Both location/meeting areas and normal meeting areas will work for getting marriages.