Has someone who has run a club in a certain other game, I can say with certainty that unless there is some kind of serious in-game support for a feature reassembling a forum, having your own is practically a must for any serious club.
Some get away with using a single thread on the certain game's website, but has soon has you get into running events, and/or start building up a membership, it really becomes a pain if there isn't a club website, with a well run forum supporting things.
Clubs are also quite a bit of work when going beyond the casual, "just for fun", not really organized level. Having good people helping out goes a long way, and it will be interesting to see what kind of tools and features PD provides to aid in administration/organization.
That said, it'll have to be set up really well, with good support, to even get me interested in starting a GT6 club. I'm not kidding when I say running a club can be allot of work.