Performance effect of indexing foreign keys
It may still be useful to have indexes on the larger table to help the optimizer for specific SELECT queries, even if you will "never" change any of the values.

However, without a lot more knowledge of your system and the types of queries you will run, it's pretty difficult for any of us to able to tell you whether you should have indexes there or not. I'm afraid it's just something you're going to have to test.

Some background in this great article by Erin Stellato:

http://www.sqlperformance.com/2012/11/t-sql-queries/benefits-indexing-foreign-keys

You also might consider avoiding the joins in some cases - when you are sure the values will never change, and eliminating the join can simplify the execution plan, you can consider just inline constants, e.g.

SELECT CASE RatingID
  WHEN 1 THEN 'poor'
  WHEN 2 THEN 'average'
  ... 
END
FROM dbo.BiggerTable
...


Also I suggest never naming something ID. If it's a RatingID, call it RatingID everywhere it exists in the model.