This is all interesting reading. I have two holidays booked in Wales for August, one near Fishguard and one near Betys-y-Coed. I live in London. Both holiday places are allowed to open. But my only means of transport is public transport. So, what to do? I am loathe to cancel. I think I shall take my chances as it seems from what I read that it is only 'advice' not to travel.
It is a shame the cost is inflated because advance tickets on TfW are no longer available.
As an aside I liked the messaging on South Eastern that you should only use their services 'if it is your only option'. That seemed fair.
You need to remember that 2m social distancing not only still applies in Wales, but is also a legal requirement. With a reduced train service, and in some cases a very reduced bus service, running at much reduced capacity (some buses having half the seats taped off, and apparently even worse on trains?), there is very little capacity. BTP have generally not been enforcing up to now as there has been no need for them to do so, ridership has been so low. But as levels rise (and they have risen noticeably around here in the last week or two), things may change if people don't maintain social distancing on trains and buses. If they start getting complaints about people breaking the law, they are surely bound to start taking action. Whether or not they can legally enforce essential journeys only, they can take action if you cannot maintain the 2m legal requirement because the train or bus is too busy.
As I say, ridership where I live, in Snowdonia, has increased noticeably in the last couple of weeks, particularly since nonessential shops reopened and the 5 mile limit was dropped. Under normal circumstances the loading would still be considered low, but with a thinned-out service and half the seats out of use on what is running, it is probably at half effective capacity. It will be interesting to see what happens now the tourists are coming back in force (yesterday was the first day that hotels and campsites could reopen, although many are still closed).
If I were in your shoes, I would go ahead with your holidays, but make sure that you reserve seats for your outward and return journeys. You then have a "right" to sit in those seats. If you are intending travelling by Avanti to get to North Wales, be aware that many of their weekday services currently seem to be "reservation only". Weekend services don't seem to be, but I would still recommend reserving. And I would tend to avoid using local buses to get around while you are here, and in particular the last bus of the day to get back (which currently might not be that late).
The major influx of visitors ignoring the government guidance immediately before lockdown had a profound impact around here. On my walk yesterday, there were still numerous posters up telling tourists to stay away, including one in the official community noticeboard. There was no need for the police to enforce closures during the lockdown, as any owner daring to open to tourists would have been ostracised by the community. Many shops around here even had signs up saying they would only serve you if you could prove you are local ("this is a local shop, for local people"). However, thankfully things are starting to get back to normal. There are a lot of people whose livelihoods are entirely dependent on tourists. Unfortunately, many of them aren't "locals".