You may hate me for being practical like this (we all love upgrading things), but if it's your commuter I'd say if it ain't broke, don't fix it! Cheap and functional is best and that's what you've got. Commuters shouldn't be upgraded except for:
The only things to add are items that increase your safety (lights, reflectors), comfort (aka bike fit, fenders), security (replace quick releases with hex nuts), and convenience (rear rack?)
If you are going to spend any money, do things that will actually matter for your *commute*. Fancier derailleurs don't mean squat - the cheap stuff works suprisingly well when maintained and fully functioning. Use them until they break! You obviously don't care about weight because you'll be carrying 30 lbs of bike locks! Why not just leave a decent quality U-lock attached to the bike rack so you don't have to carry it. Leave a second one if you need to lock up the other wheel - though personally I'd just get rid of the quick releases assuming your wheels are cheap anyway. Just don't make it convenient to steal them.
And get the flat/clipless pedals. That would be a useful addition. Just don't spend big bucks as pedals are easily removed and stolen. I'd probably use the $30 Performance Bike Campus pedals for a commuter, though the Shimanos or Mallets are surely much nicer. For convenience you might want to buy a pedal that uses the same cleats as your other bike's pedals. That may be worth more in convenience than the difference in pedal performance or price.
As for the fork, I swapped my heavy suspension fork for a cheap chromoly fork. The thing weighs about 2 pounds and cost $40 *including* installation. Ask your bike shop about Tange Chromoly Mountain Forks from their supplier. Much more efficient for street use and bomb-proof, too.
Just my "practical" two cents. You want your commuter to be fully functional, but completely cheap and *undesireable* to potential bike thieves.