How to complete a Morgan Silver Dollar set?

I have started collecting Morgan Silver Dollars and so far have purchased years 1878-1884 all graded MS65 by PCGS. I am wanting to complete the set graded MS65 by PCGS all the way through 1921 but will do so with various mintage marks/locations (Carson City, New Orleans, San Fransisco, Etc) as some are much less expensive than others. Is this a good investment idea? Will the set be frowned upon because it is from various locations and different mint marks? Any suggestions? Thanks!