A coat of linseed oil isn't hard to apply. The truth though, is that most of the windows out there that get reglazed, do not get any type of prep treatment. Wood windows have a certain look and lend authenticity to an old house. Other than that, most of the advantages end there. Wood expands and shrinks, holds moisture, is heavy, wears in contact areas, requires regular maintenance, provides no insulating value and they don't seal out the outside air very well. The most effective thing you can do to protect and insulate is to install storm windows. I was recently on a job where the homeowner had left an upstairs storm window open. The top sash of the wood window was in near perfect condition, the bottom was terrible. The glazing was popping off, the paint was peeling, it just looked bad. I still have some wood windows in my own home. The difference in those and the newer vinyl windows is certainly noticeable.
If you don't like storm windows, the best you can do is to take every precaution to make them last and to make them energy efficient. Make sure the glazing is all in good shape, make sure the window trim is caulked and that there is no opportunity for water to get behind the siding or the trim. Keep the windows painted and clean, dust will build up and hold moisture to the paint. Direct sunlight is as hard on glazing as anything, if you have awnings, try to keep them.
Inside, a little wax on the frames, just in the area where the sash slides to keep it lubricated. A free moving sash will not wear as fast and will maintain a seal for a longer time. Keep the window sealed with polyurethane or paint. When you apply the poly or paint, let the finish bead just a bit on the glass. It will eventually pull loose, but it will help seal the glass to the wood and keep air from coming in. AND, if your windows have a problem with condensation, keep it dried up. Use a dehumidifier in the room where you have a problem. The plastic film that many people use is not really good for the windows. It puts the widow even more in harm's way by sealing it to the outside elements. There is no way to control the humidity or the temp between the plastic and the glass.
If you just want the windows to last a little longer until you can replace them with vinyl, it would still be best to seal the wood before glazing, it also makes the glazing easier to get off the next time you glaze.
Anyone else have anything to add?