I included a very detailed trip report of Tikal with my AC report under the AC chat heading.

Definitely recommend an overnight at the ruins. Despite my usual do-it-myself travel style, did book it through Katie at Maya Travel, because I heard and read repeatedly (in Lonely Planet and other reliable, but perhaps outdated sources) that the hotels at the ruins are hard to contact, and they are rumored to only take reservations from local agents or tour groups. Since I was going for Easter weekend, I did not want to take a chance.

You can definitely do this as a day trip, but it will be exhausting...and you can see a lot more when the tour buses all leave, and you have the ruins virtually to yourself (and the security guards, police and soldiers).