Does SQL Server Clustering Enhance Performance? I'm not experienced with SQL Server, I'm a novice.

I'm a developer, and i think the question is more related to a Database Administrator. 

I'm working on an old legacy system where over time the Database underneath this system has grown in schema and data over a number of years. 

Some tables have around 600,000 records and there are over a hundred tables with a large number of relationships between them.

The systems performance is being severely affected,  as the number of users grows and more tables are added, the queries become larger.

The SQL Server is reporting timeouts daily and the number of timeouts is growing all of the time.

My colleagues have optimized the query plans and indexes in the SQL Server Instance to the best of their ability.

The system runs off one SQL Server Instance, running on a separate server to the where the application is hosted. 

Is there any benefit from using a SQL Server Cluster to enhance performance.

I know that its beneficial in terms of maintaining availability if one Instance goes down the other takes over..

But would the workload be shared between SQL Server Instances, i.e queries / writes...

Most importantly would it reduce timeouts?

If there are better , more optimal methods to combat these timeouts, and advice would be great.
SQL Server cluster is a fault tolerance solution it has nothing to do with performance.

If you want your load on sql server to be shared , you should be looking at Replication or maybe log shipping, direct reporting calls to that replicated /log shipped server and keep application calls to the main server. 

If your data gets too large that no matter what you do, performance is still a problem, consider archiving data to a data warehouse, in your application database (OLTP database) only keep recent records (last 6 months).  Anything older than 6 months gets shipped to your data warehouse (OLAP database). 

The moral of the story is clustering your server isn’t going to give you any performance boost, consider an alternative option.