From the way you describe it, it sounds like it's a regular gate valve. You might be able to repair it as you describe by removing the packing nut and replacing whatever is broken or stripped out inside.

The only exception to that would be a ball type valve, but those will just have a handle that makes only a 1/4 turn. Those generally aren't repairable, but then again they almost never fail either.

Personally, I would just remove and replace the gate valve with a good ball valve. Gate valves have a tendency to rot out or seize up from lack of use. I actually had one once that disintegrated in my hand when I tried to turn it off (spraying water everywhere and making a nice mess). Ball valves are just much more reliable.

Everybody wants to save money

Builders and utility companies are not in the business of wasting money, which means the main line will be as straight and as short as possible. This is a big help to you, since it will narrow your search. Walk out to the curb shut off, and look back at your house. Try to determine the straightest, shortest path between the curb shutoff and the house. Now you'll have a general idea of where the line enters the home.

Trace the line

In most cases utilities bury a tracer wire in the trench above utility lines, to make the lines are easier to locate later. If you call 811 (assuming you are in the US, though I believe this service is offered in other areas as well), they should be able to send somebody out to locate the line for you. This will show you the approximate path the line takes to the house.

Don't let pipes freeze

Because it's a water line, it will likely enter your house below the frost line. If you can determine the frost depth in your area, you'll have a more targeted area to search.

People are idiots

It's not uncommon for people to do dumb things, especially when they don't know how dumb they are. Water meters and shutoffs are ugly, and nobody wants them in their newly remodeled living space. It's possible that your valve has been walled up, and you'll have to remove some finish material to find it. Look in closets, and keep an eye out for access panels.

If only you had X-ray eyes

There are a few tools that can help you search a wall where you suspect the valve might be. A stud finder should be able to locate pipes in the walls, depending on the stud finder you buy. A metal detector will find anything metal, so that could also come in handy. If you've got a bunch of cash to throw around, a thermal camera may be able to actually see the pipe through the wall.

Where does service enter?

After reading the update to the question, and then reading through building code. It seems that it may be possible that there is not a shutoff valve where the line enters the building.

International Residential Code 2009
P2903.9.1 Service valve. Each dwelling unit shall be provided with an accessible main shutoff valve near the entrance of the water service. The valve shall be of a full-open type having nominal restriction to flow, with provision for drainage such as a bleed orifice or installation of a separate drain valve. Additionally, the water service shall be valved at the curb or property line in accordance with local requirements.

According to this, there must be a shutoff valve "near the entrance of the service". However, in most cases the water meter has to be near the "entrance of the service" too. In your case, it may be that the "entrance of the service" is at the property line, and not at the building. So there may actually be no shutoff valve inside the house.