SkyNet only becomes stupid after the first movie as a result of trying to rehash the successful formula of The Terminator. Had Cameron employed even the slightest bit of imagination, he could have developed a rousing action/ adventure SF movie that actually advanced the story instead of creating these endless questions as to why, if SkyNet could send back more than one Terminator (a direct contradication of a major plot point in the first movie by the way), it didn't send 5, or 500, back to 1984 in the first place. The reason it didn't is what Reese says - the machines had already lost to the humans, the Terminator going through the time machine was a last ditch effort of total desperation. Last ditch meaning, they had NO other options, and they certainly didn't send single Terminators back to various points in time to continue trying the same stupid stategy over and over again.
It undermines the whole suspension of disbelief for the entire story, which is why I personally ignore that any sequels exist.