Did you know that most people fill up their dishwashers detergent container to full, even though you don't have to? Most people use up to TWICE as much detergent as they need for their dishwasher - meaning you could get as many as twice the amount of washes out of one container of dishwashing detergent!
Next time you do the dishes, look at the compartment for detergent. See that line inside the cup? That is the actual fill line, so don't fill up any higher than that. And not only that, you can experiment using even less than the recommended amount to see if you get the dishes just as clean, especially if you are one that rinses dishes first or use one of the major brand name detergents.
Should you pay extra for the newer detergents with added bonuses, such as rinsing agents? Not really, they are just a waste of money unless you find them on sale for the same price as the regular version.