Mono tracks will come out both left and right channels by default, without any effects needed. Why do you want to convert these to stereo?
Just checked the "mono" track with my headphones -- and indeed you are correct. I hear it in on both channels.
So nothing needs to be done.
However, then, why does Premiere Pro have these "features"?
Thinking more about this, however, as I write this reply,I like putting a mono track directly above or below a stereo track -- and as you know, you can't put mono track into a stereo track (you have to create a new mono track, which is a minor pain) -- so that would be at least one reason to convert the mono to a stereo..... I have to create a new mono track - and sometimes that track is far below the stereo track I want to mix it with.
I also notice this article which implies you can make it so when you import any track (mono or stereo) into premiere it will be (based on your preference settings) "converted" to mono, stereo, mono as stereo) etc.
Yeah, track placement is the only reason I can think of for going mono to stereo.
I've been doing some more research....
Here's a link to an Adobe Video someone on Experts-Exchange provided re audio mapping in Premiere Pro CS5.
And here's a response I got on Creative Cow:
"Mono as Stereo" creates a Stereo file with the same audio in the Left and Right Channels.
"Stereo" Creates a Stereo file and allows you to assign the incoming audio streams to left and right channels. If you have a single mono file and select "Stereo" You will be able to select weather the audio is sent to the left channel or right channel, but not both.
As as side note, if you have a stereo incoming file, and select "Mono as Stereo" you will get two stereo tracks in your timeline, one with the left incoming channel in both left and right, and the other with the incoming right channel in both left and right.