I agree with Magnum.... the older you get, the more difficult it is to focus on the sights and target. Your eyes just lose that flexibility.
Plus, with the power of the cartridge, the Mosin will really benefit from mounting a relatively low power scope on it, especially if it will be used for hunting. If you're just ringing gongs, it's not quite as important... unless you get upset when you miss, of course.
I'm in the process of semi-permanently mounting a base on mine, where the rear sight used to be. My project got interrupted by, well, life I guess, but I plan to finish it out no later than this winter. My Mosin carbine is just too accurate and fun to shoot to leave it waiting.