If it's a purchased part, you don't need a whole lot of accuracy. ie. you don't need to worry if the edges of filletted, you don't have to add alignment keys, etc.
That being said, reduce the complexity of your purchased parts down to a part. This is just good design practice. Plus, since suppliers often have multiple configurations, a part can be driven by a design table directly; so you don't have to drill down. Reduces the load time on your assembly... The benefits go on and on.
I have attached a part for a roller that I quickly whipped up. Look at the configurations tab to see the Design Table.
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As some additional food for thought, you can also drive dimensions from a .txt file. Just insert the file in to each part (import through the equation manager) and then link dimensions to the imported variables.
To change dimensions, just change the .txt. This isn't a solution to multiple configurations though, it will just let you rapidly change similar dimensions between mating components.
ie. I have a bunch of flanged surfaces between 5 different parts. I want all the flanges to have the same dimensions. So I drive it by a global var
Devon, EIT [Mechanical]
Solidworks 2011 SP 1.0