Hi; block tester would read negative with a bad water pump. The block tester detects exhaust gas in the coolant, from a blown head gasket for example. On the stratus you can check the water pump just the same as the Intrepid, it should be leaking externally out of the weep hole next to the thermostat housing; if there are no external leaks do your basic coolant checks, plugged system, oil in coolant/coolant in oil, and pressure test. Head gasket replacement is much more costly and involved than the water pump swap; however both should be done at the same time since the timing chain has to be removed anyways. As far as if its worth it, if you plan to keep the car for several years, and it is in good shape otherwise, yes...really up to you in that area.