Another new bike!
I was gifted a 15 year old Bianchi 12 speed (Italian CRO MOL frame). It's in very nice condition with 105 indexed downtube shifters, brakes, hubs and BB. It's a beatiful lemon yellow.
The crank is a BIOPace unit. Is this worth keeping or should it just be changed out?
You may get different answers if you had posted on Vintage instead of Mechanics. If the pedalling idiosyncracies of the Biopace don't bother you and the gearing is tolerable and the chain/drive not worn then I would vote to leave the poor thing alone beyond a major teardown to check bearings, cables and housings, and brake pads and to clean and reassemble. Good opportunity to wax the paint too.
This is too nice a machine to redo as a 10spd rear.
Be sure to disassemble the hubs, bottom bracket (if cup and cone) and headset before you ride this thing. I once bought a used Bridgestone about the same age as yours that hadn't been ridden since it was new. All the bearing grease had dried out to the consistancy of rubber. I would have ruined the bearings if I had ridden it first.