There is only a certain current that flows through your electrical system, so a filament bulb can only use so much of it. You can put a higher rating filament bulb in, but it will either not work or blow after not too long.
I would recommend getting a good set of LED bulbs, and by "good" I mean $50 or more for a pair from here: V-LEDS.com. As far as I know, the only way to get brighter lighting is to go LED, or rewire your lights. Anyway, I've outfitted all my exterior lighting with their products and they give good output and are quality made.
btw if these are going in your tails, make sure you get red, not white.