Yes it would be a bit better but then as you mention, it would ruin almost all the SI derived units. That would mean that any quantity measured in previous units would be rendered invalid, or you would have to coin new names for all the units again (would probably be the safer route -- if someone takes a figure in "old" newtons as one in "new" newtons or vice versa the results could be cataclysmic.), which would then lead to a proliferation of units because of all the built-up material around the existing SI. Not to mention there are not enough letters in the alphabet to avoid symbol clashes unless you made almost all the new unit names two-letter symbols, making the notation cumbersome.Yes it would be a bit better but then as you mention, it would ruin almost all the SI derived units. That would mean that any quantity measured in previous units would be rendered invalid, or you would have to coin new names for all the units again (would probably be the safer route -- if someone takes a figure in "old" newtons as one in "new" newtons or vice versa the results could be cataclysmic.), which would then lead to a proliferation of units because of all the built-up material around the existing SI. Not to mention there are not enough letters in the alphabet to avoid symbol clashes unless you made almost all the new unit names two-letter symbols, making the notation cumbersome.

Furthermore, thinking of the long term. Rockets are getting better and better -- more and more good. That means that someday we may be moving off to other planets like Mars. Those planets will have day lengths different from Earth, and so any decimal unit we used here would no longer provide any advantage there. So either you'd have a proliferation of time units with then attendant proliferation of related units, or you just stick with the SI as it stands right now and accept that planets just don't rotate on nice standard intervals. (The same problem is encountered even if you stick with traditional hours and minutes. A day on Mars is not a nice amount of hours and minutes.)