+1 for IBO's suggestion of a test ride... last time I bought a new bike (for my wife) was in 2010 and that year Sora had 8 speeds and a wacky thumb shifter, whereas Tiagra was 9 speed with the normal shimano pattern. What that bike has is 2300 - no idea how the form or function compares. I think for 2012 groups Sora functions the same as the upper Shimano line, so I'd say at least try to get that. The main difference is usually longevity & weight along with some performance improvements that probably won't matter a whole lot to you, at least not now.

See if the shop will let you go for a 10 mile test ride... or rent the bike for a day. Riding around the parking lot won't tell you anything - it's analogous to men standing around an open car hood in the dealer lot. Oooh, look, they put an engine in this car.