It depends on the bike. And yes, a PX10 is worth it. Of course it depends to some degree on the present condition of the bike and what condition you want it to be in when you're done. The headset, for example, probably looks rusty but may still have good bearings; and so on. The only special tool you need is the Stronglight puller, and you only need it once every five or ten years, so you can borrow it. The white paint is easy to match. The decals are available. The original wheels were nice, but if you're not into tubular tires you probably would have replaced them --or at least the rims-- anyway.

I was going to make a crack along those lines....