In short, it's really not necessary or financially beneficial to have a rental car.
I figure we spent about $15-$25 USD per day on taxi fare (5 of us into town/Mega/etc. per day), so that's quite a bit less cost than a rental car. But... you lose a little bit of convenience not having a car. Not much though, considering you have some hassle having a rental car: going to rent it, park it, gas it up, etc.
The Aldora bikes saved a lot, too, as we rode up to friend's hotel and downtown a few times, which otherwise would have incurred taxi fare.
Next time, I'll rent one for our last two days or so and go to the other side. On this trip, though, it worked out very well NOT having a rental car.
