How old are the wires? Do the plugs look fouled? Sounds like you're at least on the right track, since you've determined there is no spark.

Only other thing I could think of, is perhaps your coolant temp sensor (not your thermo sensor), could be bad, which would explain your car's overheating and it's willingness to crank, but not start. A bad coolant temp sensor will throw your car's readings way off and cause the car to think it's running hotter/colder than it really is...hence why your temp gauge started going up. It also makes your car a pain in the ass to start. Sometimes you can get it started up after a few crank attempts, sometimes you can start it at all....you literally have to let the car sit there for a good while (hour or two), come back out and keep cranking it, until it finally starts. Once the car starts, you'll be greeted by a wonderful dosage of gas fumes.

But since you've already determined that you aren't getting any spark, I would think the culprit lies somewhere in that region. Even if that's the case, you still may want to take the time to replace both your coolant temp sensor and your thermostat sensor, if they are very old.