drivetrain upgrade
 

My wife is on a 1999 Specialized Globe A1. She's really liking the bike more now than in '99. Especially the geometry. That said I'm going to upgrade componentry and drop some weight from the bike. I plan on starting with the drivetrain. I have new wheels/cassette, should I hold off installing until I have new chain, cranks, deraillers, & cables/housing? or is a bit by bit method alright?

Yes, hold off installing the new cassette until you get a new chain. Unless you know for sure that your chain is still good and hasn't stretched too far. A bit by bit method is fine as long as you consider how the parts are working with each other. If you were to install that new cassette with a worn chain, the cassette would start to wear down A LOT faster.

You could probably drop a considerable amount of weight by installing 1.25" or 1.5" wide foldable tires. Bar end extensions and/or clip-on aero bars would also be nice for giving variety to hand/body positioning.

excellent, thanks. so cassette, rr derailler, chain and cranks altogether then, right? I'm also dumping the suspension seat post (since the seat is superbely padded and has healthy springs) and the adjustable stem is going Salsa style. Already riding the foldable 1.5's

Not all of that stuff has to be replaced at the same time because not all components wear down at the same time. They need to be checked for wear. How the bike is being ridden and what material(s) the components are made of are primary factors. Hope that clears things up.

Install the new wheels, cassette and a new chain. New wheels alone can be a significant change in the feel and ride. As Andrew mentioned, a nice set of tires also make a big difference.
Make the other changes you mentioned when and if necessary.
Save the rest of your cash for a night out with the Mrs.

If you replace the shifters go with 10-speed shifters, cassette, and chain. The derailleurs and crankset can be replaced later. If Shimano new cables and housings will come with the new shifters.
BTW, Campagnolo shifters fit small hands better than Shimano, but then you would need to do something to make the rear wheel Campy compatible.

Al