There is no benefit to changing to 700Cs save for the following reasons:

#1: Your existing wheels are tacoed, and you don't have a pair of alloy 27s" on hand.
#2: Your existing rims are steel, and you have a good pair of aluminum 700C hoops/wheels on hand, but no 27s".
#3: Your spare wheelsets are limited to aluminum 700Cs (no 27s"), and your frameset is sans wheels of any kind.
#4: You already have 700Cs.
#5: You want 500+ choices of tyres instead of 50+.

-Kurt