I was in the same boat as you once, and went for the GAIT analysis you mention. In my opinion this is a complete waste of time...the congruent advise I got from 2 running shops (Runners Need and Runners world) ended up giving me running knee problems and was completely at odds with what a physio (accredited by the London Marathon team) told me I needed.
If you're injury free and doing okay - be carefull what you wish for! I wasted a lot of money on crap shoes from these so called running shops.
NB in my opinion are the best. I get them from Sports Direct.