You've been chasing similar problems in other threads often jumping all over the place. An engine only needs 3 things to run:
1) Fuel
2) Spark
3) Compression / Air
I highly doubt you're missing number 3 since it does start cold. I mean you could have a valve clearance issue that only presents on a warm engine keeping them from closing all the way but I'd expect that after repeated tries to start the bike you would be getting some backfiring out the intake or exhaust or other signs of that.
Since it idles for a bit then dies hard and doesn't restart you've got to be missing #1 or #2, spark is the easiest to check (in my opinion) so I'd start there. Check spark when it's cold and again when it has died and won't restart. Hopefully you have a good strong spark in both cases. If so, move on to fuel. Since it runs for a while then dies I wonder if your float level is getting out of wack? I don't know what carbs are on your bike but if you can check the float level on the bike check it when you know the bike will start and when the bike has died and won't restart, see if it's the same. SInce the plugs are brown but not wet with fuel I wonder if the bowls are running dry?