Hi M.,
I too am running into the same situation. My daughter is in pre-school 3 days a week for only a couple of hours. Kindergarten is either full day or half day in our district.
As I am typing this to you, my daughter is making my point. I find that on the days that she is not in school as well as the afternoons after school she seems to get really bored. We do lots of things together but, I think that she needs to have different surroundings. She loves to play with the kids and talks about her teachers non stop. She seems to be thriving more from school than from being home with mom.
I think that she may be going to full day kindergarten. For as much as I may not like it, I think it will be more beneficial to her. Not to mention that her 1 yr old brother can get a break from her....LOL
Good Luck in you decision.