Firstly, welcome back to Wow! With only a few weeks until Cata it is worth seeing some of the world as it is, before everything changes! Also, as you say, people will be levelling new chars come Cata allowing you to easily find groups within the guild (with any luck!).
As for joining PCG, last night we had several raids on which I know Teem and Ruafl were both involved in along with most of the officers so your /w may have been missed amongst everything going on! One of the best things about PCG is with 400 + members we are very rarely 'in need' of a class so anyone of any class or level is normally welcome, as long as they haven't been kicked out of the guild for causing trouble and that they read PC Gamer.
My advice would be try /w one of the officers again tonight, before 7.30 is best as we have another big raid on tonight. If you can't see an officer ask any PCG member if they can point you in the right direction and if there is an officer around they will, they are generally a friendly bunch!
Thanks for posting on the forums rather than continuing to /w officers in game, if we don't reply we are normally afk or caught up in something and can't reply/don't see it pop up.