Hello,
What CAN'T you do with the 28mm???
You can shoot the same scenes with your 28mm that you can with your 50mm - and it allows you to get up close and personal if you want to. No close ups of people's noses to get an intimate picture of their facial expressions.
I used to never take the 50mm (or one of its 55mm / 58mm cousins) off my SLR. I found, but only after switching to RF, that 28mm is the perfect format for 35mm shooting. The same scenes look so much more personal and intimate with this lens. It can add an element of the surrounding you don't get with a normal "portrait length" lens.
It's also a good almost-wide lens. It captures a vehicle, building or group without all the clutter around them you would get in a wider lens.
ALSO - with the 28mm you don't have to worry about the distortion you can get with a 24mm and wider. When my Nikkor 24mm was new I shot lots of images of churches on hills with their steeples bent backwards.
That was a painful and expensive lesson, learned while shooting slides on vacation.
I recently acquired the 28mm I've always wanted - the Rokkor 28mm, f/2.0. It's supposed to be great - as I hear the Kiron version is also.
I won't get to use mine until May, but I'm looking forward to permantly locking it onto one of my Minolta bodies - and to reviews from a buddy of mine who is borrowing it until then.
Let us know what happens.
Jeff M