It depends where the weight is.
Two lbs on the wheels (tire and rims) is noticeable, but not a big deal otherwise, IMO. You notice it more picking it up than riding it.
Try this: ride your bike with and without 32oz of water in water bottles.
I would not buy a 30 lb bike with the plan to replace stuff to get a 28 lb bike. You may end up spending more than if you just bought the more expensive bike, and there may be other reasons the other bike is more expensive. So you could well spend more money and have a worse bike.
If you have specific bike in mind, post them with their specs.