You are right. If you can spare disk space for cache it makes also sense to set --vfs-cache-max-age to "forever". At least this is what I do. If something has been downloaded and I have space in cache then let it live there. Worst case it will be evicted when --vfs-cache-max-size is reached. This is off by default and makes sense to set to control cache size.
Small caveat here (as per docs):
If using
--vfs-cache-max-sizeor--vfs-cache-min-free-sizenote that the cache may exceed these quotas for two reasons. Firstly because it is only checked every--vfs-cache-poll-interval. Secondly because open files cannot be evicted from the cache. When--vfs-cache-max-sizeor--vfs-cache-min-free-sizeis exceeded, rclone will attempt to evict the least accessed files from the cache first. rclone will start with files that haven't been accessed for the longest. This cache flushing strategy is efficient and more relevant files are likely to remain cached.