I firmly believe we have too many brands. Its not helping these companies.
When we had only 3 suppliers, then different branding made some sense, for differentiation purposes, even if they weren't that different.
In marketing there is a basic concept called an "evoked set". It essentially says that consumers are only going to consider some number of brands for any purchase, and cars are no different. There are what - something like 20 OEM's now, many with more than one sub brand. No one will consider that many for a purchase.
Pontiac, Oldsmobile, and Mercury went away for these reasons. Nissan needs to roll infiniti back into Nissan - like they do in Japan. Chrysler needs to go away. Dodge maybe too, or rebrand all the imported Fiat stuff under Dodge if they like. Etc and so on.