As a match going supporter of my local side in the Northern Ireland Premier League, the things that have killed our league more than most is Sky TV and budget airlines, when i first started going to games in the very late eighties early nineties the attendances at games were 3-4 times what they are now, for our local derby games we would have 6-7,000 at them, games were regularly delayed to allow fans to get into the grounds now our derby game would have around 1500-2000 going to it, when you talk to lapsed fans and ask them why, they will tell you they save their money and fly to England now maybe 3-4 times a season to watch decent football (obviously not Stoke fans).
As the attendances in our league have fallen obviously so has the income of clubs, which has led to a drop off in the quality of football as we can no longer afford to supplement the local players in the league with Scottish and southern Irish players as most clubs had been able to do for years.
Another thing that at the time hurt our league was the Taylor Report, when it was published and the push for all seater stadiums started, clubs in the mainland UK were able to access funding to upgrade their stadiums, teams in NI were denied access to these funds but were promised that it was an oversight and would be rectified (it never was) this led to the gap in facilities starting to really widen between even the lower league teams on the mainland and those in NI, which again enhanced the going to English games experience for the former Irish League fan.
In recent years in NI, grants have been made available to teams to enable them to upgrade facilities, and this has seen a big improvement in most teams stadiums, but this has sadly brought its own problems as virtually all stadiums are now all seater even if the grounds only have two sides with seated stands, terracing has had to have been closed as health and safety rules have gotten stricter and stricter pushing unsustainable costs onto clubs. The by product of the all seater stadiums has been the virtual end of decent atmospheres in grounds were once opposition fans would be separated by fencing and could sing/goad/taunt each other all game now they are at opposite ends of the ground, this last few years young fans who have tried to bring atmosphere back to games have been virtually hounded out by stewards quoting health and safety protocols.
How do you improve the Welsh/Northern Irish/Irish leagues that is a question with no easy answer I'm afraid, in the case of NI I'm not sure it is fixable, thousands of football fans on a Saturday afternoon would rather sit in a pub and watch a Premier League game, you have no chance of getting them to an IL match, another thing in NI is we don't have Sunday leagues like England all our equivalent teams play on a Saturday, so thats thousands of football people playing that could be watching local teams, these teams refuse to move their games.
The one thing i would like to try is summer football, you no longer have the competition from the Premier League for around 3 months of the season, better weather, better pitches which should lead to better football, it has been a success in the Republic. I think another major thing that has to improve is coaching, players are not being taught the proper way to play football but again that's not easy as the vast majority of these youth "coaches" are just volunteers trying to help out and the cost of these volunteers getting proper coaching credentials is very expensive. We have been fortunate enough over this last 10 years to have qualified for Europe about 5 or 6 times and have played teams of various standards and have even managed to knock a couple out but even those that we have knocked out Skonto Riga from Latvia and SK Shkendija from Macedonia have been technically superior to us there is no reason for this two be the case as they are both small countries with similar populations to NI.
I know my post is very specific to NI, but i'm sure some of the points apply to Wales and even Scotland aswell.