Changing out Fork in 820

The RST 191 fork seems to be ok on the Trek 820 but I was wondering if it would be a waste of time and money to change it to a RockShox Judy TT or SL-Uturn. I plan on probably doing dirt trails and some small jumps (1-4ft). Do you think its worth it? Or will the RST's do a decent job?

Also I don't really like the way the stem is raised a bit. Would it be worth it to change that as well?

This bike was a gift so I haven't put any money into it. Suggestions?