Central Vacuuming: Is it worth it, and how does it compare to normal vacuuming?
I've installed several systems in new construction projects up to about 6,000 s.f., one of which was a log home. (That was interesting.)

No, you don't necessarily get better performance. It's all about convenience and not having to deal with dusty bags or canisters except maybe once a year. A really good standalone unit will at least equal a central vac powerhead.

Each brand has a specific interface. Some may be compatible, but don't count on it. You could have the builder rough it in and add the boxes and covers later, if you're the patient and careful type.

It's true that central vacs expel less dust into the home in the sense that the collection can is usually outside, or at least exhausted to the exterior. They're often in the garage or under an exterior shelter. If yours stays inside, it all comes down to specific hardware. 

Floor sweeps are great if you actually use a broom (or just want to kick a little debris in). If you're more of a hard-floor vacuumer anyway, they'd be somewhat pointless. 

"Worth it" is subjective. You might look into doing the install yourself and save about 2/3 the cost. It's not difficult and isn't as critical as drain plumbing since a tiny leak won't destroy a portion of your home. With modern standalone vacuums as great as they are cough Shark Rocket cough, it's up in the air. So to speak.

Other thoughts:


Noise is a bit of a wash. You don't have the fan motor running at the point of use, but the air being pushed through the pipes can whoosh a bit in other rooms, and the powerhead brush motor (or pneumatic impeller) makes some noise. You also have a powerful fan unit coming on suddenly in your garage, which can startle the pants off the dog. 
The powerhead and hose assembly is a bit cumbersome to use and store. Since the hose has to reach from the inlet port to the other side of a typical room, they're much longer than what you'd find on a traditional portable canister vacuum. Think laundry-basket sized bulk.
The inlets can leak slightly during use or snap shut a bit when the system is activated. Again, noise in rooms other than where the thing is actually being used. 
Some folks end up buying multiple powerheads, one for each level of the home. Plan for that potential cost.