As mentioned earlier, doing anything at your speed is satisfying and relaxing, especially when traveling. If you are asking is it worth renting a car in Costa Rica, then yes. It will provide you with freedom from the collective tour busses and public transport. You can follow your schedule and stop whenever you are tired and need to stretch or enjoy the view. Having your belongings with you in the trunk and your family relaxed in the backseat, asleep or looking out the window, is all worth it. A private ride will also allow you to go off the beaten path and find gems hidden in the Central American nation. You can backtrack and revisit areas that excited you with a rented car, which might not be possible with tour groups.
Renting a vehicle might seem expensive, but it is cheaper than taking flights to the destination or driving in a bus. It might be slower than the plane, but the views are further enhanced when you stop and take in the view and even some pictures. Gas prices are not very high and are affordable. However, the roads differ significantly the further away you move from San Jose. They drive on the right side and use Kilometers to measure distance. Most roads are not paved and contain potholes, so drive carefully. Additions like insurance will depend on yourself if you require them, but taking higher clearance vehicles is an advantage if you will do offroading. Renting a car during the offseason would save some money on your budget as they are cheaper than when there is higher demand during peak tourist season.
Most car renters are on their second or third visit. Usually, the good spots are further away from the road. With the weather also affecting the road, it is not advisable to travel during the rainy seasons as most roads have no bridges and rivers pass over the tarmac, and mudslides occur frequently. Trying to fit around bends on high ledges with oncoming traffic is tricky. The roads have no rails and would require some getting used to. The jungle and hills cause the streets to be windy, and animals often cross the road, so watch out for jaywalking animals. Sedans are the most popular car types for hire, and they would get around comfortably, but are not good very far off the road.