I think you mainly should focus on 'sequence of returns' risk. Your first decade in retirement is what will set up the rest of your results, and you'll know long before you hit even 20 years of retirement if it's failing.
Being adaptable and proactive during that timeframe is just about all anyone needs to do.
CAPE can be helpful, but how it's measured is not the same as it was, so it's not historically consistent. Don't have the link, but there was a detailed rundown on it that made the case that the historical avg. of ~16 should probably be considered ~20 as it's measured now.
So with CAPE ~29, things are overvalued, but not quite as much as it seems. In 30 years, it almost never dropped down to that old avg., much less gone below it. Even after the 'lost decade' of the 2000's dot com bust and huge 2008 crash, CAPE only touched ~15 for a blip before shooting back up. Unless you think that means we're in for a GIGANTIC reversion that will devastate the market for the next 30+ years, I think CAPE's not very helpful or that predictive going forward.