It's certainly a worthwhile project, IMO. Even lowly French bikes from this era can offer an excellent ride quality. The French seem to have unlocked some secrets to bike geometry during this era. Many of the lower end 70s French bikes offer a nice stable, all-purpose ride, with good tire clearance, decent wheelbase, and road-absorbing fork rake (amount of curve in the fork). That said, if the bike has sat for too long--you said it hasn't been ridden in 30 years--all of the grease has probably dried out. If you proceed to ride the bike now without greasing the bearings, you will likely ruin the ball bearing surfaces. It's not terribly difficult, but it does require a little practice, know-how, and tools. Taking it to a co-op is a good option, if you have one nearby. After tending to the brakes, it's important to put fresh grease in the hubs, bottom bracket, and the headset for starters (the heasset is perhaps less important, but worth doing, too). Pedals as well if they are serviceable. The cottered cranks make getting to the bottom bracket a little more work. You should also add some oil to the freewheel by dripping oil onto the back and/or front while spinning it. You can open up a freewheel and add grease, but some argue it's not worth the trouble. Fresh cables & housing is money well spent. Paying a bike shop to do these overhauls will probably cost you more than the bike is worth. Do it yourself and you'll make your dad proud! Warning: Fixing and riding vintage bikes can be habit forming.

By the way, here's an example of what dried out bearings look like. This is an Atom freewheel from a 40-year-old French Mercier, probably similar to what youhave on your bike. There should be grease covering all those little balls. Without the grease, the bearings and bearing curfaces (cones & races) will develop "pits" and need to be replaced.