Well that is interesting. I'm not sure what I'd expect - they weren't a large tribe relative to the settled population, but they were a tribe and Arian christians for awhile. I don't think they destroyed much, or built much when they settled in France and Spain. Is there no difference in population centers, weapon or burial finds, coins etc. between 425-525 ? I don't know a lot about their subsequent activities in Spain, other than they had most of Iberia under their rule for awhile.
I'm not near my little library, so I can't give you any references right now. The role of the bishops is well known (the church on the peninsula held several synods, and arguably the eventual victory of the anti-Arian field was proof of that continued influence), and the continued preeminence of the bishops of Merida, Cordoba and Hispalis (Seville) is also well known. Toledo rose in importance as a new political center, but it was not a sudden thing. Bracara in the northwest may have also gained importance as the center of the suebi kingdom, but it's hard to say whether that was cause or consequence. The southern cities lost political influence for awhile as a result of being conquered by the byzantines and thus separated from the polity that ruled the rest of the peninsula, but they continued to be important, priority targets that were eventually re-annexed by the visigothic kingdom.
The visighothic kingdom had its fair share of civil wars, several between kings and their sons (in that it was already showing a typical medieval pattern), including Hermenegildo's rebellion (well known because he ended up proclaimed a saint), but the most destructive warfare for civic life seems to have happened around the early to mid-5th century and is related to the anarchy during the last years of Roman imperial power. Namely, those punitive expeditions sent by Aetius in 453 and already discussed here, the repression against the bagaudae which themselves had targeted cities and apparently even sacked several important ones. The building of city walls was probably due to the threat posed by that disorder, not to the "barbarians" who were actually being used by what remained of imperial power to suppress it. I've also seen mentions of "mauritanian" (north african, where we now place Morocco) raids across the straits of Gibraltar before the Vandals even arrived (don't recall where, sorry: history is just a hobby for me). Imperial power, apparently, was also breaking in the westernmost portion of its african provinces before the arrival of "german" barbarians.
What exactly caused the final breakdown of imperial power in Hispania is unclear, but I won't be surprised to see someone argued that the source of the anarchy was in armed bands who resulted from the decades of warfare there since Constantine III's ineffectual invasion of the peninsula. No emperor ever again managed to reassert imperial power over the whole of it. Why, I don't know, but it seems obvious that what they lacked was a loyal and large enough army to sent there.
On the burials thing I'll try to get some from a colleague of mine who's an archeologist and has been looking into that era lately. She was my sole source for that, actually.
Also, as was commented in another thread, it is useful to remember that ancient states were in essence military machines dedicated to the extraction of the taxes with which to pay them so as to be able to collect further taxes! Thus military failures meant a smaller tax base, which in turn meant a smaller army and reduced ability to collect taxes. I'm not so radical about this as, say Finer in his "History of Government" (the man was a typical liberal obsessed with denouncing any other type of state...), and I can see also instances of what we might now call "nationalism" in many ancient wars, but for
empires it seems to have been true. Too many years of civil war, lack of decisive battles where the victor takes all the loot, and an empire ends up collapsing into an anarchy of small lordlings... I don't know how many years of uninterrupted civil war the Empire had survived in previous crisis, but by the mid-5th century it had had too many.