LED tech has come a long ways and gotten a lot cheaper in the last couple of years. The Koreans (Cree) especially have been pushing the envelope. There ought to be amber blinker LEDs that are brighter than stock incandescent available from somewhere.
Edit: In fact, looking at the page at http://autolumination.com/1156_1157.htm I would expect the "3 watt super star" or the "Eagle Eye II" to be the brightest of the bunch. I have a custom flashlight that uses a white luxeon led like the one in the Eagle Eye II and it is blindingly, painfully, bright.