It's not better to create a new part. Don't worry about the new records. As long as your maintaining your indexes on the database, you won't see a performance hit. This is what a database is built for.
Besides, new part or old part, it's the same amount of rows/records for the reference.
I agree with Lee CS Young. I wanted to add that while a record for each where used is created for each reference regardless, if you create new "uniquely named" parts there is a row for each in the documents table that wouldn't be there otherwise. Create once, use many times.