I like the global tu reservation idea, If I have to walk my soldiers across the entire map for the instance of a sole remaining bloodspider. I would only want reservation when nearing the target and rarely after setting individual allocations do the reactions mode gets used. A 1-click global Reservation generally allows for some minor tactical refinement before the assault.
On the individual TU reservation quite often I find I have not allowed a spare TU for directional positioning, so I have effectively stored TU's whilst "not" peeking around a corner. Perhaps some options like save "10 Tu's" , "15 Tu's", "20 Tu's" maybe of benefit.
On the business of automation, is it not possible to have a continue to target feature whereby if you select a point on the other side of the map the soldier will automatically head to that point if he has unallocated, unreserved TU's at the end of the turn, or on a global "continue action" button.