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I think that's pretty much it - flex and heat resistance, up to 200°C even. The latter will make soldering a lot easier (for amateurs) of course... and may even save from a short circuit (provided it's quickly caught) because of wires melting together.

I don't think multi strand or single wire will have a whole lot of impact on general electron flow.
Overall surface dimension and intrinsic material resistance should be most decisive there.

Heat resistance, flexibility & general "coolness" are definitely the key words here.

I can understand the idea of electrons being more abundant on the surface of metals (That's why they look shiny) & that more strands gives more surface area (Thus more available electrons), but it all falls over when you consider 3+ year old wire that's tarnished & sucked up all manner of dirty water, oil, grit etc (By capillary action), all the things you find around toy cars, & now you're looking at each strand having to carry its own current (Because it's difficult for the electrons to pass from strand to strand due to the pooey surfaces), & here we are at the "2x bits of 5A fusewire side-by-side won't carry 10A between them" scenario.
To illustrate my point, you only have to grab the wiring on a vintage car or battery after a run, & note how much hotter the particularly dirty-stranded wire gets (Y'now, the stuff that's so bad it's impossible to solder). This heat buildup is all wasted energy, power that went into heating the wire & not into turning the motor.
Incidentally, that's one of the reasons I hate crimped connections - they're quick & great when new, but cause all sorts of spurious "No continuity" problems after a few years

Thanks Edou, I've ordered the 16awg stuff to see how it looks. Most of my cars, although they are in running condition, are just shelf dwellers. They're bog stock complete with mechnical speed controllers, tin can motors and so far as batteries go, I have one 'test' battery and the others are still in the box they came in. I was mainly aiming at the visual part of the wiring for the SD's but on the runners were the ones I wanted to stop the cracking discolouring. I ended up ordering it from Hobbyking, along with a brushless motor esc combo for the WW2 lowrider. I got a Turnigy trackstar something or other, just their basic set up, then noticed on their forum people having trouble with setting them up, ah well maybe I just bought myself another paper weight. I know jack shoot about brushless other than that they hoot. I put one in my Losi mini Baja and it went nuts right from the start, never had a set up card with it. The one in the WW2 Wheeler is bigger and has a card but it's nowhere near running so I haven't even done what I think they called the initial set up. I'll probably get it all finished, charge it up, then back flip it and trash all my good work.