The perceived better performance of Sora over 105 might perhaps be due to the under-bar-tape-routing on the 105.
(Much neater certainly, but some quite small radius cable bends)
Lack of maintence maybe, I just installed 105's worlds apart. I have always had Sora on the viking (being poor) and after two upgrades from 7 to 8 and 8 to 9sp then the right shifter failing, i debated between Tiagra (which I can't comment on never having used them) and the 105 because of the cable routing issue, I am glad I went with the 105's, though still getting use to the no cable in view thing.
I might add it is probably not worth getting shifters off
ebay ect as the two I got, the right 8sp and the 9sp set both developed faults the 9sp had only done 2,500 miles or so since being fitted in April, this is not to say Sora are faulty as my originals did over 12,000 miles.
Tiagra's can be had for just over £100 and 105's about the £130-140
