I think the principle of the UK nations running their own processes (health, education etc.) was a sensible one, and if it was being run as intended there would be far fewer issues. Unfortunately, as said by PP, it's been completely hijacked by nationalists who use all their power to further a separatist agenda and tend to ignore the basic functions like running Scotland (and actually haven't even taken control of all their devolved powers because its a bit too hard).
If Scotland were to vote for independence (and I personally think its a terrible idea) the Holyrood set up is clearly not fit for purpose. It lacks the basic checks and balances that an independent legislature requires and too much power is in the hands of the SG, resulting in the many examples of sloppy, poor quality legislation that comes through here. Some kind of additional chamber would be needed in those circumstances.