Just a nitpick, neutrons aren't blasted into the nuclei of fissile isotopes. The faster a neutron is going, the less likely it is to cause fission. You want slow neutrons.
Depends what you're going for. If you have the fissile concentration to support it a fast-neutron chain reaction has lots of benefits: more neutrons per absorption in fuel leads to the ability to breed fuel for millennia or alternatively get lots more energy out of nuclear waste. Fission product poisons don't affect fast neutrons that much so you can get way more energy out of the fuel in fast reactors.
Indeed. In a thermal reactor, the energy of the neutrons is moderated down to the reactor operating temperature, and is typically a few tens of milli-electron volts (some tens of millions of times less energetic than when they were produced). These slow neutrons do impart a lot of energy when they are absorbed into a nucleus, but that's because of their binding energy into that nucleus. Due to nuclear shell effects, they add slightly more energy to nuclei with an odd number of neutrons, which is one reason why 235U can be fissioned with thermal neutrons and 238U cannot.