I was just looking over Lyle Berman's PLO chapter from Super System 2, and he says you should "never raise from up front." So okay, it's easy to LOL at that now, but I know some pretty successful live pros still buy into that idea.

Coming from an online background, I was reluctant to open limp at first, but with some more experience I think it's pretty clear that the best way to go is to have a raising AND a calling game from early position, and be prepared to use whichever is best suited to the situation. Your raising/calling ranges don't have to be perfectly balanced, but they shouldn't be totally transparent. If you don't have a limping game at all in full ring live PLO, I think you're probably giving away a lot of EV.

To address your points...

1) Agree, up to a point, but I don't think this is that strong of an argument. In my experience, weak players usually play a ton of hands for a limp or a single raise -- up to a point, the hands they play are just the hands they play, and they don't seem to care much whether it's 1 bb or 4 bbs. It's not uncommon for someone to play 75-80% for a limp, and 50-60% for a single raise. It's nice to get them in the pot with those 80% hands, but it's also nice to make them put in 3 more bbs with a 60% hand, so I think it goes both ways here.

2) Strongly agree. I think this is a much bigger deal. I see the kinds of games you're describing all the time: everyone is comfortable putting in the first raise, but there's almost no 3betting. In a game like this, raising and limp-calling are usually different roads to the same thing: a single-raised multiway pot. But if you have a premium hand and want to force as much money is as possible pre-flop, limp-raising will on average let you get way more in than open raising.

I'd say the first two questions I ask myself when deciding whether to limp or raise are 1) How much do I want to get 3bet? 2) How likely is it that someone will 3bet? and I build my strategy from there.

Coming from online background open limping might seem bad but should definitely be a part of your game while playing at tables where noone ever folds.
I've tried it out myself and it seems to be working out pretty well :) 

When players are just horrible postflop you should be looking for an excuse to play as many hands as possible, why not doing it while playing smaller pots than?

I have a very simple strategy for EP in games like this, although it's disgusting exploitable if people pay attention (luckily, they don't).

Strategy looks something like this: Raise your monsters/really strong hands that flop great multi-way (your good big pairs, big rundowns etc.) and limp other stuff with the potential to gin flops (shitty big pairs, mediocre suited aces - AT86 for example - etc.) hoping to get in cheap (you can limp/jam your bad AA hands depending on stacks if the action is re-opened for you).

You don't wanna limp everything, that's stupid, 'cas hands like AA98ss, AKQTds, JJTTds etc. are worth more than a limp (push your edge and build a pot for your good flops). However, getting in super cheap w/ the hands that tend to miss should prove crazy profitable if people are too dumb to realise that single high-card flops are gonna be ALL YOU (you'll set-over-set people a lot, but your range is so telegraphed a good player should be able to get away crazy easy. But then if these were good players, the games wouldn't be soft).

Postflop, just play for value. Bluffing will almost always be spew so simply try and max on the flops you hit and go from there. People will give you enough action that you should do very well indeed. Your red-line (non-showdown winnings) may suck, but who cares if you are printing money!

What should the strategy be if there is one MANIAC at the table. Usually my regular 9-handed PLO game look something like 2-3 good regs. 4-6 Calling stations and 1-2 guys who just POTS, POTS and dammit POTS again. And god forbid if somebody repops him once then he goes over the top :D.