Isn't the "/spawnpoint" command in the latest version of minecraft? I'm currently working on a map right now with no mods, command blocks and /spawnpoint work fine. If your doing "/spawnpoint <x> <y> <z>", I'm pretty sure the coordinates won't work if you enter them with decimals (ex: 134.5, 64, -342.5). If your using command blocks, here is a suggestion to set a spawnpoint at a certain location:
/spawnpoint @p 200 64 334. @p chooses the closest player, so this would work perfect for single player. "/spawnpoint sets the spawn at the coordinates your standing at.
Then again, you could type /help and see a list of the commands...
Edit: Also, I am not sure if people mentioned this, but you could make a huge square far away from your creations that is loaded with trip wires, and when they spawn on the tripwires, it sets their spawnpoint and teleports them to where you want them to. Just another suggestion to help.
I don't know all of the things you have tried, I'm just saying what I know. I totally understand your frustration man, hope this helped.
I recommend using Single Player Commands. It has a /setspawn button that I know works because I tried it. Use that an it will change spawns. Also you can change your speed /setspeed (number here) and stuff. Type the /help and it tells all. Good luck!
Just saw that you didn't know if it changed everyone's spawn point. Well try Single Player Commands mod still and post download link here, then ask if you spawn in X....Y....Z..... Worth a shot!
I read someone saying to reduce the radius of the possible place to spawn around the spawnpoint. I think that the solution is inside that. You have to find, not only a way to set a precise spawnpoint, but also to set a reduced radius of the possible place to spawn. If your room have 8 blocks radius and the spawn radius is 16, then the players car spawn outside the room.
Agree MapCritic. Funny to see this thread pop back up. After all this time the mystery remains. I thought I had this problem fixed, but lo and behold I am spawning right back at the same spot. This should not be as tough as it is.
As others have been saying, try "/spawnpoint". I'm not sure if it'll work when opening to LAN, creating a server, or making a world save, but it's worth a shot. (according to my understanding, LAN relies on personal data, so it should work then. If you're making a world save... it may still work, as you're copying all of the world data.) Since you're interested in the world save (I assume, as you're sending it to a YouTuber), you could test it by quick copying the world folder, and logging in on the copy.
If that doesn't work, isolate the 16x16 chunk players spawn in. Rise to the highest point, and build a platform covering that point (it should be 16x16). Make sure there isn't a block above that platform, and you may want to world edit out anything below it just in case. Then, cover the area in tripwires, and outside of the chunk connect them to tripwire hooks. This way, the player won't spawn on the hooks or blocks above them, ruining the design. Then, simply redstone the hooks to a command block with the command "/tp @p <x> <y> <x>, with the coords of your desired spawn point. If it's built right, players should spawn on the tripwire mat, trigger the command block, and appear in the correct spawn point. You may have to world edit some parts of your map to do this, but at most that should take a few minuets of work and some lag. Above all, make sure there's nothing above the mat players should be spawning on, that would ruin it.
So I was working on this really cool resource pack a while ago, but bad progress nonwithstanding, I think I found something much better... I'm probably gonna release a couple of maps soon as unrelated well.Until we meet again...