At some point, it will stop working again. If you have an oscilloscope, you can see how the signal degrades as you pile on sensors. It's not like it's a very clean signal to start with. Long cables will add to your woes because of the capacitance of the wiring. Lower value pull-up resistors will help in many situations. As you already saw, you could go as low as 1k if needed since it was working until you got it below about 500 ohms. The sensors were only designed to sink 4mA which means even 1k is a little small.