Well, if you set yourself up for a system that encourages failure, you basically have to live with what you get.

Plenty of people will stick around in a guild even if they're not top priority for loot or have an even chance for loot because they want to be part of a team. A team involves 25 or 9 other people, and usually a few subs on the bench as well and as such it can NEVER be about you, it should ALWAYS be about the guild. If you don't set your GUILD up for success by rewarding the people who are both successful AND regular raiders, you're probably going to be nothing but a pack of loot whores and when the loot stops so goes the guild. (this can be a RL situation that takes a few people away, guild drama that chases someone away or just plain hitting a wall in progression but rest assured people start to bounce when they don't get their loot if they're not team players).

So yeah, don't reward your lowest DPS with an even shot at loot. It's going to make your solid performers grumpy that new people/crappy performers get the upgrades and in my experience most of the worst (ie: the ones you can tell that don't really care) tend to be the guild hopping sort that will take your best in slot trinket and jump ship to some other guild where they can annoy all new people.

You owe it to yourself and your guild to use a loot council or rank restrictions on loot. Find the team players, upgrade your guild before upgrading the players on a player-neutral basis and you'll find success a lot easier.