I'm not quite sure what the Luiz signing is validating exactly? I think pretty much everyone agrees that is one of the most ridiculous transfers ever, so if you're saying 'they did it, so the precedent is there', I'm not sure what to say to that.
As for Vermaelen, I wouldn't say I watch his every game, but of the few English games that i do watch, Arsenal's tend to be the most. And over the last 2 years, I have of course, seen very little of him due to him being injured like ALL the time. And when he has played, I can tell you he hasn't looked good. He seemed off the pace and I think he was a good reader of the situations and his positioning was one of his strong points when he was doing well at Arsenal - I just don't see that anymore. Also, a close friend of mine is a die hard Arsenal supporter of many years and explained exactly what he thinks of Veramaelen, and his view (and the view of many other Arsenal supporters he says) is that if they got anywhere near 15m for him, it would be one of those take it and RUN kind of deals...
Hope its more clear why a lot of people don't want him now..