I just got Ultegras and so far it's a mixed bag for me. I'm used to Time ATACs so setting up the cleat was a bit different, and it sucks how fore-aft is not independent of foot angle or side-to-side.
I was (and still am a little bit) considering Speedplays but it sucks how much extra **** you have to buy besides the pedals/expensive cleats. I walk in my shoes a decent deal, so coffee shop covers would be mandatory, and the bearings for some odd reason require periodic grease gunning (why can't they be like ATACs and just have great seals to begin with?), so that's another $38 to spend. Say you can't get the cleat lined up as far back or forward as you want (a possibility for me because my SPD-SL cleats are pushed nearly all the way back), that's another $36 to spend on an extended base plate kit. Seems like a lot to put on top of an already expensive pedal just to save 100g and get some better cornering clearance and adjustable float.
As far as the small platform of Speedplays, a carbon sole would most likely negate any supposed loss of power.