Hi Greg, Yes I would probably opt for an electric vacuum pump if cost is the same, but I would expect it doesn't draw much power, nor enough to warrant upgrading the alternator. Most alternators have plenty of unusued capacity. Replacing water pump with electric is different tho, Cooling systems is one of the few things that I do know loads about. A close friend of mine won plenty of speedway trophies with an engine that I helped develop, and it ran an electric water pump. We modified the cooling system heaps but I was never sold on the electric pump part.
Even if you allocated 100 amps to the water pump that still only equals 1200 watts, belt drive water pumps use far more power than that and they use it to good effect. A cooling system gives you thermal tuning. No point having a computer tuning to engine temperature if some cylinders are that temp, others Cooler and warmer. Literally the warmer ones would be running rich and vice-versa. I saw a kit developed for a common 6 cyl inline motor that guaranteed 10 percent better economy and power. All it did was upgrade the water pump and some plumbing to equalize temperatures.
Automotive cooling systems are such a disappointment. The pump impellers alone tell the story, you only need a little logic....or a water pump off an industrial diesel and you'll soon agree with my disappointment.
If you wanted to improve things through your cooling system I would suggest a modified impeller to pump more water and cavitate less, then drill very small hoses into the back of your motors coolant jackets highest points and vent the hoses to just under your radiator cap. Theres most likely a benefit to be gained and really all you're doing is upgrading your automotive cooling system to commercial engine cooling specs.
I have done this many times but never have I done it around fuel economy checks that I have documented.