Susan, you might want to check to see if you have any clear finish on the wood. There is a real quick and simple test for this which is to put a couple of drops of boiled linseed oil, from the hardware store or home center, on your wood. If it beads up, there is a clear finish of some kind on the wood and it would surprise me if there was not. If it soaks in immediately, there is no film finish. A film finish would protect the stain, if there is any, and not allow any bleach type operation to work, so it is a good idea to find out exactly what you might run into.
I do not think that removing any of the wood, by sanding, sandblasting,or other abrasive methods is appropriate if you can find any way around it. There is only so much wood there and no reason why it should not last forever. There are some natural processes that might be happening though and that is that wood naturally darkens with age. Cherry is famous for this and the process is very pronounced. This happens to other varieties of woods in varying degrees and conditions but it does go on under film finishes.
Have you tried washing the wood with Dirtex and a damp sponge? Years of cigarette smoke and other dust and dirt can build up so slowly that you do not see it occur. You might try this in a spot that is not easily visible. Damp will work fine and sopping wet is too much.
Also, I am not sure that you realize what else occurs with a process like sand blasting. The years of disturbed dirt and smoke will come off the walls, along with some wood dust, and make the rooms that you did unliveable for a few days. Cleaning will be a constant chore or months and you will still find pockets of sand years later. Sandblasting is a great process if done outside or in an industrial setting. I don't believe that I would ever try it inside my house.
You might check on these alternatives and let us know the results.