My mum had a phase of getting bad cramp, and the doctor prescribed her salt tablets. Since my mum has always eaten crazy quantities of salt, adding it to her food by the spoonful, I'm quite certain lack of salt is NOT the cause of cramp!
I've also heard quinine is good for cramp - the stuff you get in tonic water. But as my mum has always been partial to gin and tonic, I have my doubts about that too!
Sorry, I'm afraid I can only tell you about what doesn't work, but I don't know what does...
Forefoot and midfoot are funny terms, really. I understand both of them to mean the thick, padded area between the arch and the toes. Forefoot is the front of that area, towards the toes, and midfoot is the bit you land on if your foot is more horizontal, nearer to the arch.
'Flat footed' doesn't necessarily mean the same thing as landing with your foot horizontal. People use the term to mean having a low arch. Traditional thinking says this is a bad thing, but these days I don't think it's seen as a big deal.
The toe problem could mean your shoes are too restrictive. It's worth bearing in mind that feet swell up a lot during a long run, so a shoe that fits you at the start may not fit you after a few miles! Also, you need to have room for your toes to splay out when you land - some shoes are too narrow in the toe box.
If you decide to invest in new shoes this close to the race, it's probably best to go for your usual brand in a larger size, and give them a good road test to make sure they're comfortable. It's risky to change anything at this stage, though. I'd wait until after the race, personally.
I would definitely advise against trying anything new at this stage in your training.
Altering your running style is something to do carefully and slowly, as you can easily injure yourself when you start putting a strain on different muscles etc. Even if you change from incorrect to correct form, you need to give your body time to adapt to an unaccustomed way of moving. It's best to do it when you don't have a race planned in the near future, as you may have to cut down your distance and pace quite a bit.
Good form is generally considered to involve a forefoot or midfoot strike, with your foot directly underneath your body and your knee soft. Opinions differ on whether you should be upright or adopt a very slight forwards lean (from the ankle, not the waist). I do the latter. You should concentrate on landing lightly and softly, picking up your foot quickly. Cadence should be around 180 steps per minute. That's it in a nutshell, but there's a lot more to it than that. Worth reading up on good form - good sources are sites about barefoot running (although you don't have to run barefoot to do it).
And following on from Ian's post above, here's an interesting article which makes exactly the same point.
For me, all we can say is that the right footwear should make it easier to run in the correct way - provided we put in the effort ourselves.
The danger comes when we rely on marketing messages as a source of knowledge - like the ad I quoted in my last post. Reading that ad, you'd be forgiven for thinking all you need to do is wear the Free Run+3 shoe and you'll get all the benefits of running barefoot. In fact, you need to study good technique and make a gradual transition. If you don't, you're at serious risk of injury.
I'm a massive fan of barefoot and minimal running, and I really believe it can help us all run better. I just hope that misinformation doesn't lead to everyone rejecting it out of hand.