I think it's worth it, but not everyone would think so. It really depends on what convention it is, and if there is anything worthwhile going on Sunday at the convention. It's always good to have extra money left over, though. If your group doesn't have a lot of money going around, it might be wise to just forgoe the last day.
Also, why is the parking $40 for two cars? I'm pretty sure that there are cheaper options available, albeit a bit further away.
SacAnime Winter*, AOD**, Fanime
Unknown at this point
* Dependent upon whether I'm feeling better, or if I'm back in the ER again.
** Dependent upon interests, time, and money