is it worth installing cam in stock 318?

You can pick up 50 HP with a cam change and still have a fairly smooth idle. You can get stock 340 performance valve spring for around $50 a set that will handle most street cams you would want to run in a 318. I run the factory 340 cam in mine it's a nice upgrade there are alot of nice streetable cams for the 318 that will boost power nicely and not affect fuel consumption very much at all.