The Ertiga is wider, taller no doubt. But, Mobilio being shorter will have its part to play on Dynamics front with less body roll. The one you might have seen is the media stage car, the production version which i saw in showroom did not have any bad finishes that we saw in media cars.
Sheet Metal is thin because to increase efficiency. It doesn't mean that car will not survive crash. Sheet metal will not save people, but its the crumple zones and other internal bits which saves. Again having owned so many cars, i will say that Fit & Finish of Honda cars are better then its rivals. Majority will not agree on this unless they buy a Honda car. Criticizing is easier while justifying is tougher and has more meaning when done.
Now coming to the premium pricing. Maruti Suzuki will price its products lower compared to rivals always. When that happens, the new car when launched(Mobilio) seems overpriced. I will fully support Honda for its pricing. In coming months, I'll can see Ciaz being priced considerably lower then City. When that happens, people will say that City is very expensive without even bothering to have a glance at it. This is Indian's mentality. And to get a product successful, Maruti must price the cars lower then it rivals. If it doesn't then that car is a flop(Ex. Estilo,Astar,Ritz,Versa,SX4,Kizashi,Baleno,GrandVitara,).