You're mixing up a lot of different things here.
1) "Top dollar" is tricky to get away from, as shown by the court actions after the failure of Railtrack, A "fair price" (i.e. market value at time of proposal) has to be paid, or you'll be looking at the govt spending tens of millions in the courts.
2) "Upgrade"? For a lot of customers, just having the infrastructure properly maintained would be an improvement on current standards!
3) Shareholder profits: The big problem here is that governments are just as likely to use profits from national utilities as they did previously, rather than reinvestment in that particular national utility - in other words, profit from one sector would be used to finance other sectors that aren't particularly profitable, but are a "social good", and that will leave such industries open to attack by free-marketeers and other economic illiterates.
4) Unless a nationalised power generation industry could find funding for a massive increase in our gas and oil storage capacity, we will always be prey to these ridiculously-high eye-popping rises - we don't have enough capacity to even gently blunt the pain of those rises. Our gas capacity is just over 3 weeks' supply, and that's after it's been increased! We need to do what the Scandinavians do - have enough stored gas to cover half of autumn and all of winter, 20 weeks supply.