Worth Splitting MySQL Server Into 2 MySQL Servers To Increase Performance
Your RDS is coping with your write load but if you want more scalability, separating the read and write load is a good idea: they have different work patterns and probably have conflicting performance tuning needs. 

Once you have decided to split then you are free to choose a different product to handle the incoming raw data for the daily write load.  Why not choose a storage medium that is more optimised for writes?  Consider sending the daily the writes to a DynamoDB dynamodb table.
As your cron jobs are already written then you know how you will query the raw data so this can help you structure your DynamoDB table.  You can autoscale dynamoDB to cope with changing or bursty loads.

You can also create a TTL on the raw data so that as time passes and the summary data is more relevant the raw data is deleted, or even send the older raw data to S3 for cheaper storage once it is no longer 'hot'.