I agree. In our guild, those that have viable offspecs are constantly ASKED to respec to make up any gaps or maximise the situation. It would be complete nonesense for them to be asked to play a roll and then get that roll side lined along with someone's alt or other less useful multi-spec classes. (druids being the best example)

DKP is fair IMO. The rest of these arguments are around "officers" attempting to micromanage how other people play the game.
You raided and you spent the time, you get points. You deserve those points more than some other clown who has either spent all his or not raided as much as you. How you spend them is up to you. All is well.
In the "master loot roll" methods, some new guy on his main can out roll a sweet piece of gear on some guy who has been waiting about for this particular piece for ages. This guy might have passed for 3-4 weeks on other crap because he is already geared up and thus been a core member of every raid. (and this is actually a RL example in my current guild)
We institute a 2 week "roll like an alt" rule for new 80's, but after the 2 weeks they only have to average twice a week to roll on anything. Not even slightly fair.

The only suggestion I would make to DKP is one that services the guild's need to equip people. I would give a blue->purple upgrade a bonus amount of "free DKP". (Call it a subsidy)
The same for main vs alt or main/needed vs other spec.
Thus you can actually weight in the need for the guild to max out their mains and alts, but allow grizzled vets to pick up gear they want if they do the hard yards.