Undelivered Letter only gives 25 gold and 1600 XP (with 2x XP) - you can only carry 1 of these at a time, and they are pretty rare to come across - perhaps they could get a little bump?
I just took a look and you should be getting more of both, but it might look weird because both reward types come in sets of two. Experience should be 800+5000. 800 is the original reward plus 5000 as an increase added with my quest reward revisions, total 5800 (or 11600 in double EXP periods). Gold should be the original 25 plus an additional 85, total of 110. I'll take a look, tho. Maybe the reward sets aren't combining properly, or it's not displaying both even though you may be getting them. I'll probably merge each reward type into one lump just to be safe. Issue #67223 The fence aboard the Jack of Diamonds gives identical rewards to the town crier. (Her data literally points to the town crier's reward assets.)