Grant- I have a front rack that prevents aero bars, and don't like my stomach to be folded in half in a tuck. My neck also starts to hurt after looking up for a while. And I kind of just want to build a weird bike.
Renault- Ah yes, we call it a curb. Usually here there is a
short ramp from the sidewalk onto the road so it can be traversed somewhat smoothly. The alignment of concrete slabs varies, but if it's really bad I can just choose to ride on the road in most places. I've never ridden a recumbent on the sidewalk, so it will be a learning experience. I'm sure some technique adaptation will be necessary.
Over half my daily commute is on surface roads (riding an upright), so that won't be an area of concern. The other part (a mile) is a 40mph (65kph) four lane road, where I ride the sidewalk when possible since there is rarely foot traffic. Bikes are only technically allowed on 35mph or less in Michigan and I have gotten heckled for riding on these higher speed roads-
even in the dead of winter when it just snowed and it's the only passable route.
Moral is, I'll ride wherever I need to ride, and motorists will be angry no matter what.