I've also been thinking about how to take profit from guild benefits, but I'm not sure how to do it. To get experience you need to do quests, kill bosses with people of your guild (75% or more) and win battlegrounds (also 75% of the team must be from the guild). So there are 4 options:
1. Get into a big guild and just benefit from what others do (they also benefit from you, as you will generate money for the guild when
Cash Flow is reached). This is dangerous in the sense that it's more probable that someone sees that you are botting than if you were in your own guild bank.
2. Buy a guild and kick everybody that's there. I really doubt that guilds would do that even for a really big amount of gold, especially those guild that are more progressed, that generally already have lots of gold. Maybe later in the expansion this idea could have some sense.
3. Try to level your own guild. You should have to do lots of quests, which is viable when levelling, but after that, unless you do dailies... And I haven't seen any profile for dailies. Another options is having characters from different accounts, so you generate more guild experience doing quests (as you do them at more characters) and also can join battlegrounds and do dungeons with 75% or more of the people being of your guild. I doubt Instance Buddy is capable to run alone dungeons botting the 5 characters of the party. Maybe in very easy dungeons, but I don't know if those give guild experience. And joining a battleground with so many bots is just a joke, obviously (and it would be impossible to win any).
4. Create a guild of botters. This would be similar to the previous option, but having more than 1 person there, so there could be lots of bots and generate experience faster. It's dangerous in the sense that you have to trust in other guild members, because they know you are botting. Also, if other people starts seeing that people from this guild is botting, it may cause Blizzard to investigate the whole guild.
So I think the best options are either 1 (particularly if it's in really big guilds, where you can go unnoticed easier) or just forgetting about guild rewards.