I think its developmental and a lot of 4 year olds do this. DD did and it drove me nuts, this was when she discovered she could get out of bed at night. she used to come to my room and get me to tuck her back in and tuck in her bears. We just had to ride it out. In the end a night light did the trick and a final reward of a bedside light.
I also think maybe its time to get rid ot the nap and do quiet time, for us its with a dvd and maybe make bed time earlier, at least half an hour. It took 6 months to break the habit with dd. She would come in my room and scare the living daylights out of me by tapping me on the arm and I would wake up with a jolt, this made me madder than anything and I got to the stage where I dreaded night time. We also did a happy sad face chart.
Now we have EW, due in part to having to be up at 6.30 for school so she does it at the weekends as well, going to tackle that this weekend if I can find a battery operated digital clock, cos she is wakening ds and going in his room when she wakes.
At this age you have to be even more inventive and try whatever works. Bribes usuallly work quite well.