I know I've got a very one-eyed opinion on this subject, but I REALLY BELIEVE that it IS important, and that it IS a fashion item. The shirt isn't just about us and our colours, it's about people in Japan who watch the Premiership on telly and want to buy a shirt because they like it, rather than because of the team. This is why I always make so much noise when the new kit's come out or a new deal is announced.
When Nike presented to Man Utd, Peter Kenyon (at the time) said "It doesnt matter about the design, we always sell 500,000 (yes, that does say 500,000) shirts". Nike advertised it and sold it through their retail network and Utd sold 2m (yes, that does say 2m) shirts in a year. That sort of money pays for a Wayne Rooney every summer.
Who was interested in Cameroon until they did the whole sleeveless thing? (Where's Ryu when I need back up?) What are you opinions on the England shirt (given that it's an optional buy for most rather than an emotional one like the Villa shirt)? The design counts, and it makes money. The same goes for the brand of the supplier, and the sponsor.
Wolfsburg sold 2000 shirts in the UK, just because they had a VW logo on the chest, the St Pauli shirt which was sponsored by Jack Daniel's is worth a mint on the internet, and so on.
I know that for most of us as normal fans, as long as it's claret body and blue sleeves it's ok, but in a BUSINESS and PROMOTION sense (which is what we hammer Ellis for all the time), the kit design can be critical in term of raising funds.