I don't agree with locking people who aren't in gangs out of gang bases. Raiding gang bases as a solo PKer or in a party is a good way to get noticed as a serious PKer by gangs, or a good way to kill some time if you're bored. I'd wager that a 5 person party would stand a good chance in a raid against a gang any day of the week. So locking them out just doesn't make sense and seems like it'd have more of an adverse effect. When trials got locked out of gang bases I remember how boring it became.
I do agree that money rewards for gangs is a good incentive though. I don't know why people have been so hesitant to do it. People can make 30K+ in a day from mining, so even if you were giving away 5k per day to the best PKer in each gang I can't see that somehow being an economy destroyer.