Redesign basic Mysql storage architecture
In my opinion, you should use an SSD if you are facing performance problems. Here is a 120 GB drive for approx. 64 Euro (&lt; 100$ US). This will keep your application ticking over for a couple of years without any need for a redesign and performance should substantially improve for minimum expense.

Down the road, if you are ultimately deciding to move to a DW scenario, may I recommend PostgreSQL as your DW server over MySQL? MySQL is good for read-heavy web-facing apps, but not for DW type work. PostgreSQL has CHECK CONSTRAINTs, SET operators (INTERSECT, EXCEPT), CTEs (Common Table Expressions) and Windowing functions (all of which MySQL (incredibly) lacks). 

Traditionally PostgreSQL was not strong on the replication, clustering and connection pooling front, but that has changed.