Yes, it does matter imo. You're better than most - I suspect you've even been to Old Trafford and seen a game or two - but you're still part of the process which leads to the decay of football's local links and proud history.
You're little better, if I'm harsh, than one of those 80s saddos that festooned themselves in Dallas kit and talked as if they were one of the "Cowboys' most deserving fans - it's the same globalised glory hunting instinct that leads to football's worst excesses. Were there really no local clubs most deserving and needing of your support, no other local links that tie you to other clubs. I'd like to give you the benefit of the doubt, but there again you're first instinct was to slag off Reading's comparatively small support and talk of your first match being a cup final, which doesn't exactly get away get away from the glory hunter accusations.
I don't know, I quite liked the way Liverpool played as a kid - hell, they won everything after all. I think I even had a club strip as a nipper. But I'd never dream of supporting them as an adult - I'm a Londoner for christsakes and the whole concept of supporting a club largely because they were successful when they were children seems bizarre and more than a little mercenary. Don't worry - I happily take the piss out of people close to home on a regular basis too, including a few plastic paddy Utd fans down thepub...