That's an interesting thought. If you merely want to dispose of it, then you can just vent the steam in chimneys on an overflow valve in your steam tank. However, it does seem like a shame that you can't use it to charge up your accumulators/surge equipment.
So a priority turbine might make some sense, but I feel like some people are confused about how these power systems work already. Some people think they should use priority electrolyzers for energy storage, if they think of using it for energy storage at all. Some assume that they will be able to actually generate more net power with steam than it took to create it, even though it doesn't make any physical sense. And I think a priority turbine will add more confusion for people who barely understand the current tools. Usually when you get to the point where you are mass producing that much benzene you have your energy situation pretty well sorted out, so venting the steam isn't too big of a big deal.
Maybe priority turbine could be introduced during chemical engineering, by the same tech as combustion chamber 3. People who make it that far should have a good enough handle on how the components work to not get the wrong idea about how to use it. And that's also the level where you're likely to be scaling up chemical production enough to have a growing problem with benzene overproduction.
Benzene is just the tip of the iceberg for priority turbines. If you compress air before air separation, you are likely to end up with a huge supply of compressed nitrogen as a byproduct, and that would be nice to be able to have the option to produce energy with and not just store energy.