I've always found the marine layer/convective connection rather interesting. I do sometimes wonder if too much emphasis gets placed on the marine layer...during the spring/early summer I can certainly see it playing a big role, however, I think it also depends. First off, the marine layers usually aren't relatively thick...but I'm sure they still do slow down the upward acceleration of parcels through this layer, however, when it's hot and humid or when you have steep lapse rates these should be enough to overcome that.
I wanted to use this for my senior thesis but I did not have enough time but my thinking is that the biggest culprit for us (outside of weaker lapse rates) is lack of stronger dynamical support and large-scale forcing (though these tend to be greater in NNE which is why like northern ME does very well for severe (IMO). But down this way we often see thunderstorms die and it gets blamed on sea-breeze...I don't necessarily agree with that. I think what happens is the storms start to outrun the better forcing/dynamics which gives the aided boost into keeping convection deep. Otherwise, convection is just relaying on large surface CAPE (needed to initiate the convection) and meh mixed-layer CAPE (which helps the storms build in the vertical and when there is enough we get the pockets of severe). But when you're only relying on instability and weak forcing/shear the instability is enough to build it and the lack of the latter prevents it from doing much more.