you don't encourage individual participation when you say 50 members have to reach the indy requirements to get the guild goal (only perhaps in top 3-5) - for all other guilds it will be the opposite.
If you really want to encourage peolpe give extra rewards for hitting the wall x times (perhaps in combination with the normal indi-goals). That way you would help the guild spirit. Now everyone will be hunting the indi-goals and the same 'stupid' members that bought orbs for the guild will now be forced to hit the wall even more often....
well done....