The three main parties should invite the SNP/Plaid Cymru to their regional debates because they are a group of people. Everyone deserves a voice in their government, so these people should be given the opportunity for theirs to be heard, as well as given a more fair and balanced debate outcome.
Every voice in politics should be heard, even the minority voices. Brits deserve to hear all points of view, including the controversial ones. Regional debates are where dialog and political discourse start. Every party should have a place in society so voters can see what choices they really have when it comes to election time.
All parties should take place in regional debates no matter what their political affiliations. SNP and Plaid Cymru don't necessarily agree with EU nationalists who think Europe should be stronger with all regions on board. SNP and Plaid Cymru's voices should be heard even if they aren't mainstream. Welsh and Scottish independence is just as valid as siding with the expansion of Europe's hegemony.
No, the three main parties should not invite SNP/Plaid Cymru to their regional debates, because it is distracting to have third parties present. Those parties do not have a popular following. It takes away from the message of the three main parties, who do not have as much time to discuss their platform. The others need to find different ways to get their message across.
The three main parties does not need to invite the SNP/Plaid Cymru to their regional debates. The more parties involved would not be good for the debate. Adding more parties to a debate would only complicate the process. Instead of normal debate protocol where one parties defends the statements of the other, adding another party would give two parties ganging up on another.