Local Decisions or National Decisions?

I was just reading the debate about the "de-centralisation" of government starting to happen under the new government. What is funny-ironic is that the plethora of opinions about the subject prove the whole problem with the debate - too many opinions.
It might be stating the obvious but it is too common for people with important roles to miss these important facets to goverment whether local or national.
Firstly, the national government is useful for providing management over a larger geographical area. Railways and motorways cannot be managed locally because they are too large. Likewise for more localised services, these are too far removed from central government and are better handled locally to suit localised needs. The needs in the Highlands of Scotland are not the same as those in London. However, the real crunch point is that there is no black and white line between what should be managed locally and what should be managed nationally. Traffic lights on motorways although part of a larger plan can cause problems locally so the local is affected by decisions made hundreds of miles away.
Of course, the other problem whether local or national is how you decide on actions to carry out. Should this building be allowed planning permission? Well the people who live nearby probably say no, the council should not reasonably object and if there is something commerical involved, the council will want the extra money that it will bring in to the area ditto for schools, hospitals and industrial estates.
This then alludes to the age-old question as to who decides? How do you give weight or merit to someones opinion? If I object to a gas pumping station because it will "spoil the countryside", especially if I live nearby, is my opinion anything other than a "not in my backyard" (nimby) view or is it reasonable and important? Of course, one of the things that should happen is people should not be allowed to object without alternatives. You should not be allowed to object to a building or planning application etc without specifying what the applicant can do instead. For instance, "they should build it on that land instead of in the country" which the applicant can counter with, "that would cost £50M more" which leads to objective argument. If people object to a planning application such as "I don't want him to build an extension, he should buy a larger house elsewhere", then the objection might be upheld even if the house move would cost more.