I'm not sure if this is the best way to handle a multi device scenario, since it will flood the VC history especially if you use allways-on devices like a wall mounted tablet. Is there a way to "push" data from VC to the website?
Probably you could have VC write to a file and the Javascript could poll the file, but first VC would need to know that a value had changed in order to update the file. If VC is not the one changing it then it can only know by polling, which brings us back to our original problem. Anyone trying to completely replace a web UI-based home automation system using this technique is probably going down the wrong path. We are pushing some simple tools beyond what they were designed to do.
But honestly, do you really need to have your sliders always up-to-date once per second? I think not. Most of the time you would want to set them and then they will be at the correct value because you set them. Nime5ter's solution for reading the values seemed good to me for when you want to check the current value.
If you are going to poll them, I would do it once per minute at the most, but if you have 6 sliders we are back down to approximately 10 seconds... It is not just the history window that is the issue, VC can only do one command at a time (generally speaking), and any other commands generated by events or voice commands will have to wait until the polling command is finished before they can execute. This by itself might not be a problem, but when you combine it with all the other crazy things people are doing you are bound to run into problems.