The average consumer and the average retailer don't care about the techie geeky stuff that you find so important. They want an instant exchange that works.
And they do have it. Instant transactions that are safe enough for everyday's expenses. Only you here seem to fail to understand how it works. Greg Maxwell, one of the most active and senior Bitcoin Core dev, has taken quite a bit of his precious time to explain it, repeatedly.
IMHO you seem to be here more to push an unsubstantiated claim that Bitcoin is impractical and cannot compete with traditional means of payments (i.e. credit/debit cards and/or cash) than to educate yourself. Your condescendance regarding 'the techie geeky stuff that [we] find so important', considering that you started yourself a technical discussion in the 'Development & Technical Discussion' section, can only reinforce that suspicion.
What exactly is your point here?
I understand about the unconfirmed transactions. While not ideal, it's an acceptable compromise for some.
Energy usage of the network is a far, far bigger issue (i.e. question 1., which feeds into question 3.)
Regarding your question 1, you could run the bitcoin network today on a regular computer - in fact that is essentially the way it happens with full nodes, they all keep copies of the blockchain which along with the software (which defines the protocol to a large extent) defines the network. Then energy usage would be negligible. It has nothing to do with the number of transactions per block, the limit could be 10 times higher, probably 100 times higher without a large change in energy usage. Maybe 1000 or 10000 in a few years as Moore's law continues along. I doubt it would double, but even if it increase by a factor of 10 or 100, it would still be negligible compared to an air conditioner or a small building.
The tradeoff there would be the security of the network. The amount of hashing power is what secures the network, so you need a lot of power to protect the integrity of the bitcoin network and blockchain, this is the "work".
There are two components that we're discussing here: running the network, and securing the network. In short, the number of transactions is not what uses the energy, it is the number computers (be they CPUs, GPUs, or now ASICs) securing the network.
Regarding number 3, I do not believe that centralization is inevitable, no. As you stop orders of magnitude improvements as you had between generations, e.g. CPU->GPU->(FPGA?->)ASIC, it is much easier to predict profitability of a miner. I believe as that time approaches, it will be easier for individuals to return to mining because they will not have to hope that they get a machine in time to have a ROI and just depend on luck to do so. With CPU and GPU mining, we were not dominated by large concerns running farms. Could hashing become concentrated? Sure. Pools could be an issue, but miners can easily switch pools - or use p2pool. Could it occur because the value of the bitcoins in the network becomes so large that it is smart to do so? Sure. I don't believe it is inevitable though, it is an open question. Ask in 10 or 20 or 50 years and the answer will be clearer.
Regarding number 2, you could have a sidechain with a faster confirmation time or any other number of solutions if you wanted some confirmation for a small transaction quickly, although as has been stated this is really unnecessary for many day-to-day transactions just as using a counterfeit detection pen on a $1, $5, $10, or $20 bill is unnecessary (and I've used $50 and $100 bills and no one has checked them too) and just as you do not need to copy the ID of every person who purchases from you using a debit or credit card. At this point double-spends for small purchases are unlikely to be profitable to try, and unlikely to be successful. And if they were occasionally, it is part of the cost of doing business.
BTW, you should not dismiss the difference in definition between transaction and confirmation and all the other technical details if you truly want to understand the network and the implications of suggestions. If you truly are not trolling, think about what people are explaining here and the fact that there are a lot of technical details that deal with many issues.
Is bitcoin perfect? I doubt it. With innovations in the technology - few of which are trivial to implement in a running network (it is like upgrading an airplane at 35,000 feet) - it can be improved and become closer to an ideal system.
:-)
* Somewhat simplified in a few spots.