I think your thinking is a bit off base as to why they aren't used, let me try to cover them:
You said you see three advantages to wire spoke wheels:
Actually if you think of the amount of money it takes to create one, you've got extra time in manufacture (individual parts), assembly (gunna be a lot of man hours), and trueing the wheel. All of these add up to a lot of money. What does it cost to to make an alloy or steel wheel? Production time is way less and most, if not all of it, can be handled by machine.
770GBP does seems like a great price. That's about $1200 in the US. I bought a set of new repop 18" C6 Z06 rims (to fit P275/35-18 tires) for a little bit more than $400. Remember, when a manufacturer makes these rims, they get mass quantity discounts, which nets it for them much less than what we are going to get on the market.
Realistically, I don't know the weight of a wire spoked wheel, but you'll have to realize, these are made out of steel. Aluminum spokes would probably not stand up to the requirements, though it would prove well in weight savings. Aluminum does not have the tensile strength steel does, so I'm pretty sure it would not be used. Both the outer and inner portion of a spoked wheel has to be built to handle the spokes, so they don't pull through, so these are going to be made of steel as well. There isn't going to be much if any weight savings over an alloy wheel.
While a bicycle may use spokes, it's because they don't support the weight a car would need to support. Rider and bike together are much less than a car in comparison. In order to support the weight of the car, the wheel has to be a lot beefier to deal. You don't have solid wheels on bikes unless you go to exotic materials like carbon fiber, but then it's cost prohibitive to the average rider.
While you can take spoked wheels apart to fix them (replace spokes for instance), there is a bit of an art to making them right again. It takes skill to do this. It exists, but it's not cheap. Rebuilding them would more than likely cost more than it would to replace an alloy one, especially if you are a savvy consumer and were to replace a damaged alloy with a used one in good shape. Then there is the aftermarket, which is most likely cheaper yet.
You can repair alloy wheels. If they are not completely destroyed, getting them welded and machined is usually not an issue. Again, I don't have the exact costs of either, but this is very readily done today (can get it done in most metropolitan areas) at a nominal fee. Finding someone to make/repair your spoked rims would be a chore in comparison. Most likely you'd need to ship them off to make it happen.
I'll one up you on this why they aren't that popular to own today:
I don't know if you've ever tried to clean a set of spoked rims, but it takes some effort. It's not easy. With today's chemical cleaners, it's easier, but you still have to get between every spoke to get it clean. Five spoke alloy wheels are much easier.
Really, chromed spoke wheels are usually considered (at least in the US) to be something off of a 70's era smog boat pimp-mobile. Most people wouldn't get caught dead with them on their car. Mind you, this is just my opinion, but I believe the stigma holds true.
From my point of view, the only reason you might see these on a car in this day and age is due to it being a niche market. Some people out there go for a certain look/feel for their cars. I'm not going to begrudge them that. I learned a long time ago, people make cars the way they like them. I like my car the way I like it. I'm not going to duce on someone's ride because that's what they like.
Because of the aforementioned reasons, I don't think you'll see them mass produced for cars anytime soon.