Where drying time is a concern stick with the moisture cure polyurethanes. They actually catalyze to set when moisture is present in air. Cure time is as little a 2-hours between coats and 12 - 18 hours for traffic. (its OK if its raining) Avoid the oil base solvent dry polyurethane that can take a LONG time to dry and is not as durable. Your better paint store can advise you on suitable products.
The spit shine is a method of sealing the wood. There are other ways to do it (filler, sanding sealer). Shellac is a good wood sealer and minimized penetration by subsequent coats. I have matched up floors in a similar situation where an addition was involved. The tough part is using a tenon saw to join the floor as tightly as possible. Also, you really want to avoid a continuous line in the floor where new floor meets old floor.
The existing floor is a good indicator of how the additional floor will wear, and as you noticed, most damage or patina is confined to the finish. I think wood floor hold up pretty good to kids, but not so much their dogs.