What about having the option to dump the value cache to file system on shutdown with the possibility to pre-warm the cache based on that dump on start-up?

Even a rather small value cache utilization of a couple of hundred megabytes may be based on hours of database queries on start-up.
The desired functionality of dumping and pre-warming the cache(s) is mainly intended to be used in user controlled circumstances only.
However I could even think of ways of implementation that could speed up start-ups after crashes as well.

In the end it should be optional.

While the real cause is related to value cache, other caches might possibly benefit from this too.