I think it's important to realize the impact that the Romans continued to have in this period. not only by virtue of the fact Constantine's church was still a major power but also the fact that they had left some amazing examples of engineering.
Obviously the church at this point was a major powerhouse, not only did they hold a great deal of economic power, but they were also one of the more convenient ways a king could bring together the various tribes and factions of western Europe together under on banner. It seems that people always want to belong, the Romans realized this and worked to instill the various peoples of it's far flung territories with pride of being a Roman citizen. With the fall of the Roman empire many kings sought to unify their European subjects as christian. This of course gave the church considerable political power. That power of course helps in generating revenue in the form of taxes. Another factor that helped to bring the church to power at this time is that it was pretty much the chief repository of knowledge and learning in Europe at this time. The bulk of literacy and schooling at this time was found within the church.
I think the church provided pretty much the link to the older roman culture and art. With the exception of some of the illuminated manuscripts produced in various areas that show some of the indigenous tribal/celt/norse influences, I think that most architecture and sculpture really tried to emulate the older roman examples.
This may seem like a different take on things but I really feel like there are two major factors in the development of what we think of as gothic architecture. One is the desire to emulate the grand roman feats of engineering, the second is the fact that they had to do it without concrete. Mortared stone is a whole lot less forgiving than concrete when your trying to build soaring arches or cavernous barrel vaults. If you want to build big you have to have strong frames. If you put these frames inside your building you lose space and it's less grand. If you put your frame on the outside it's going to compromise structural integrity. That's were you start adding buttresses and such. That's what happened a lot of the design feature we think of as "gothic" started out as structural support than spawned a new style of aesthetics. I think if they had had concrete we probably would have old cathedrals that looked a bit differently.