I rode with Sora for years, and don't think this is as big an issue as you make it out to be. I now ride a 105 ten-speed, and fundamentally my shifts are no quicker than they were before. Here's why: When you are in the drops in Sora, the only shift you can't make is upward, toward higher gears. You can downshift from the drops in Sora. In fact, with higher end shifting systems you often have to make two shifts instead of one: one to shift, and another to trim after the shift.
For the upshift in Sora when in the drops, keep your non-shifting hand in the drops, and quickly move the other hand to the hoods to make the thumb-shift, and then put it back in the drops again. Don't change your body position. The whole movement should be seamless and quick, and shouldn't affect your aerodynamics at all. Perhaps in criterium racing this could be an issue, but it shouldn't be in normal club or recreational riding. Bar-end shifters wouldn't be any quicker, and also can't be shifted easily from the normal drops position.
Also, to me it's not worth it to upgrade from Sora to Tiagra. You aren't going to gain enough to make the upgrade worthwhile. Sora is just as durable, and when it's time to do a lot better than Sora, it will be time to do a lot better with the overall bike: wheels, cranks, etc. Going from eight speeds to nine is also too minor an improvement to make it worth it to change all of the components that would have to be changed in order to do that.