Living in southern England - Scottish University?

I work at one of the Scottish universities and there are at least as many English students as Scottish, there's no way they will feel out of place. The stories about discrimination are difficult to take out of context, it was part of a discourse about how the government in Scotland could deal with funding tertiary education differently than England and Scottish students not going to university if they had to pay in England. There is no easy solution but none of it IME is representative of a deeper problem, and not your problem - something for the politicians to sort out.

As for worth it, in what sense? If they are into outdoor sports then probably worth the extra travel a couple of times a year to have your hobbies really close by. If the struggle with the cold weather down south, then maybe not.

Re interviews, it depends entirely on the subject and the uni. For example, Edinburgh do NOT ever interview for medicine, but Glasgow seemingly always do. They do things differently for some of the other subjects.

Edinburgh University has recently been in the news for saying they were giving some additional weighting to students who live in Scotland, but that's the only story of discrimination I've heard.

Not sure why Scots should be considered insular - the UCAS site has some stats about applications (not acceptances though) figures here near the bottom. By my reckoning, 86% of English students apply to English universities, and 88% of Scottish students to Scottish universities - doesn't look like a significant difference to me! Given the total size of the institutions in both countries, Scotland also has higher levels of applications from N Irish, EU and non-EU students.

Re Travel - not my DCs but friends - both at St Andrews.
One friend and her DH would drive up from Surrey - stopping over in Yorkshire on way up, then drive all the way back the next day
Another used to go up by plane with her DD to Edinburgh in order to get two lots of baggage allowance (in days when baggage allowance was always included) - then travel over to St Andrews train/bus (?) then reverse journey home. She lived near an airport fortunately!

I have heard stories of Scottish Universities discriminating against English applicants. Dunno if it's true: can you research the statistics?

How will your £9000-per-year DC feel, living amongst the we-got-it-for-free?

Your DC is more likely to meet a broader spectrum of people elsewhere. The Scots seem a bit, ahem, insular when it comes to tertiary education.

Db went from South Bucks to Edinburgh and loved it. I went to a midlands uni and I recall the admissions tutor asking why I wanted to go so far from home. I pointed out the fact that my parents considered it to be a day trip compared to where db was!

We lived in Kent and my DS went to Strathclyde. Perhaps not a good example as he ended up dropping out after the first term :( Ultimately it was just too far away and he was homesick.