I was CFI at Cumbernauld for a few years and I can assure anyone that Glasgow App on 119.1 is often extremely difficult to contact. 119.87 is often not a huge amount better in certain areas, though it isn't bad. Certainly in the area to the North of the Campsie Hills, unless you are above 3000' then you have no choice but to talk to Scottish, not Glasgow, even though Glasgow were constantly asking us to contact them.
These problems have been pointed out on numerous occasions, but nothing has been done about it.
As Xray Alpha mentions, GLA are sometimes loath to let people transit their airspace. So I wouldn't welcome any increase in their boundaries. Though anyone who enters that class E without talking to anyone needs their head seen to, but surely there is a more a need to look at all te airspace around there, not just changing the classification of one bit?
Edinburgh have never been an issue and I have never been denied a transit, though I have taken some odd routings, but that's just part of the fun!