I'm trying to work more toward selling prints but clients still want the files. I guess I need to raise the price of the files.
This issues has been discussed back and forth (or maybe it's just me

)
As I see it, the issues are that when you give/sell the digital files, you are taking the final product out of your hands. The client could print the images on typewriter paper with a $30 printer (or worse, Wal-mart

) and when the prints look bad, it reflects badly on us...without us even knowing.
Also, you could be loosing out on potential print sales because clients are making/ordering their own prints.
When I do sell the files, I stress to the clients that not all labs are the same. I haven't yet, but I may make up a sample display with a good print and a bad one, just to scare the clients into using a good lab. Or even if they use a cheaper lab like Costco for example, I tell them that they can request that the lab reprint their photos if they don't look as good as they should.
As for the lost potential...I guess you could try both and carefully analyze the numbers to see just where you stand...but my basic advice is to sell the files for enough to make up the profit for what you estimate the prints sales would have been. You may miss out on what might have been a huge print sale, but you also get paid for what might have been a small print sale....and if your selling of the files actually brings in clients who are specifically looking for that, then you are ahead of the game.
For wedding and portraits (wedding especially), a lot of photographers I know are using custom products as something to sell the clients, even though they are selling the files. For example; high end custom designed wedding albums are selling for hundreds (and thousands) of dollars, which is often on top of the wedding price. Sure, clients could design and order an album with the files you give them, but some of these photographers are quite good at the design and most of the 'high end' album companies only sell to professionals so it's not something the average client could get anyway.