Maybe. I quit using Champion spark plugs back in the early 70's over almost new plugs dying. Still won't buy one,or even put one in my lawn mower if you give it to me.
For the MOST part spark plugs either fire or they don't,but I did have a 1 cylinder lawnmower engine drive me nuts once trying to get it to start. I was just about ready to take it to a lawnmower pro to get it fixed because it was getting fresh gas,and I could pull the plug and ground it and it would fire. I decided to try a new plug first to see what happened. It fired right up. Damn thing would spit fire all day out in the open,but the instant you put it under compression it would die. Once again,a Champion spark plug. I got it for free because the guy that gave it to me couldn't get it to start.
I have no idea how that could be related to the engine starting after sitting out in the sun with the hood up,though. Your problem HAS to be related to a fuel supply problem.
When it is sitting and cold have you tried taking the breather off the carb and manually moving the carb linkage to see if it is spitting fuel down the intake port? If not,your float needs to be adjusted by either bending the tin arm,or replacing it if it leaks.
If it pumps fuel without the engine spinning over after sitting all night,the float is ok,and your problem is related to the choke. PLEASE note that this test MUST be done ONLY after the car sits overnight. You could have a very small leak in the float that would cause it to dump all the bowl gas down the intake overnight,but fill the float so slowly that once started in the morning the car will continue to start fine all day.