is it worth installing cam in stock 318?

Well, I am assuming that you have the earlier, non-Magnum 318 (the 'LA' version). There was the car engine, with a real static CR in the low 8's and then the truck 318 with SCR in the 7's, but neither is high compression. The Magnum 318 (5.2L) was a higher compression, in the upper 8's IIRC, but that is not HIGH compression really. So the PO was.... let us say.... 'misinformed'.

If you are cruising around, then by all means, you have to pay attention to low end torque. Low end torque and wide torque band make cruising 'workable'; you have 'go' anytime you push on the go pedal, not a bog waiting for the RPM's to build until some torque begins to happen. So your focus on a mild cam is suitable. Take some time a look up so called 'torque' cams and the smaller duration cams like Lunati Voodoo's and such. They all will be shorter in duration, and the ones I like best will be as high as possible in lift. Then pay attention to the LSA.

The on thing to be careful of with a short duration, very high lift cam like the Whiplash is to make sure that that valve train can take it. Stock valve springs will bind, or be to close to spring bind, with that amount lift and will allow the valve to float at higher RPM's. So you surely need a cam kit with springs. And, you need to be sure that the valve retainers do not hit the valve stem seals and valve guides with higher lifts. That is one reason that sticking with a lift in the range of .450-.460" works well; it is safer for things like retainer clearance. A lot to think about!