For more challenging bandits and less bizarre reactions, you should go back to play 34.11,
It's right, that the creatures (not only people, but animals, too) are far more aggressive and that the entity-related reactions are working, but there's one actual bug which kills 34.xx for me.
The duplication bug where, if someone is killed in a town or hamlet, he/she/it will always come back - and therefore you're getting a kill list with names multiple times in it. You can't clear anything of living beings. I stopped playing Adventure Mode in 34.11 and rolled back to 40d, till 40.xx came out.
And actually I can't play the older versions anymore because I would miss all the improvements which were made/re-implemented (like sites for dwarves/elves/goblins - even if some of them are broken).
And this leads me to:
so I keep marching on to bandit camps expecting a fight on my hands but when I meet them they just don't fight me
You can set the discipline for creatures/people to 1 or 2 in the raws and as soon as you'll do it, they will start fighting back (to some degree).
If you want to force someone to fight, just grab him/try to wrestle him and suddenly they defend themselves and you can start your actual attacks.
Yes, these tips are just workarounds (and it's sad that the whole concept is bugged) but it works and leads to some of the experiences you encountered in former versions of DF.