Upgrade for 10w signal bulbs?

[d3vi@nt]

I'd like to make my stock signal lights brighter, but prefer not to go the LED route. Are there any options at all? Stock bulbs are 10w. If there's a 15w replacement, would the difference even be noticeable? How much higher wattage can one go without causing electrical issues? Would a clear lense be better?  I'm basically looking for inexpensive ways to increase signal visibility (besides using hand signals 

[Raux]

I'm running the 21w bulbs, and although brighter, they don't work long term. ie after about 60sec sitting at a light they stop blinking.
too much power draw
i'm going to go LED. but there are Halogen bulbs available as well that I think are brighter.
My best suggestion stick with the right wattage or change out the blinker relay to match the new wattage.

[stopintime]

You most probably have a solid state relay in the instrument cluster - not much you can do about that.
I've been told it can handle 21 bulbs, but it will take another few weeks until I can confirm that.

BUT - the next step up is 21 and there isn't room for them in stock lights.