99 chev Cavalier engine problems

There are a few things wrong and i'm wondering if it is worth trying to save this car. First off when it idols, the entire engine block vibrates about 2 or 3 inches forward and back. Second from what appears to be the connector for spark plug 4 (4 cylinders) there is a slight crack in the metal and it is continually making a click click click sound and occasionally I can see a blue spark arching from it to a small bolt between the connectors for plug 3 and 4. I was told a while ago that the spark plug head for cylindar 1 was cracked and that coolent was leaking into it but I do not know how credible that is, as my family has had many a dispute with the mechanics that said that. It allready has 215,000 kilometers on it and I don't know if it is worth trying to save this engine, or if in the long run a rebuilt or new engine would be better.

could someone please give me some non biased advice.
yours truely
~david