nailing over spider web cracked shingles

My house was built in 78 and I have no tar paper either...My situation is a spider web type of cracking of the shingles mostly on the sunniest side of the house. Can I put a second layer over this or should I do a complete tear off. They are asphault shingles, and if I can should I put a layer of tarpaper of them 1st. It's a standard type roof no frills just 2 sides and a peak. No leakage as of yet, check by contractor.

 

I'm not a big fan of adding a second layer of roofing over an existing layer. Sure, you can do it, and sure, it's legal to do, usually. But that is just adding a lot of unecessary weight to the truss system supporting that roof, and the second layer of roofing just doesn't last as long as it would without that layer of roofing under it. Sure, you save a few hundred dollars in tear off expenses, but you have to pay the $4,000 to $6,000 to reroof in 15 years rather than 20. Then you say your existing roof has no felt under it. No, I would tear it off, lay down 30# felt, then put on the new roof.