OK, here's my take on this, having had both in the past:

The Pro edition has a few extra aircraft, and also contains Image Tool and maybe some other program, Image Tool enables viewing of texture files in formats that some photo editors and viewers cannot.  You don't need Image Tool unless you repaint.  The extra aircraft, well, there's tons of stuff everywhere as we know, so that's no big deal.

As far as any appearance differences, I did not notice any.

So in summary, they are identical.  In my opinion, MS should have just come out with one edition.  As usual, it may have been a marketing ploy.

If you've already got the standard running, don't waste time with the Pro.  The fact that it's called "Pro" makes it sound better, in reality, they are exactly the same.  I would have noticed differences if the Pro edition was a step up.

You might consider FS9 (FS2004) if your computer will run it at decent frames, there are visual improvements there over FS2002, but it takes more resources. 

I don't know anything about FSX, so cannot comment on that.

Thanks for everything.  I'm thinking one day I may just buy a cheap used version and just use it to grab the aircraft off of.

Thanks,

Mike