I've never bought a foreign NT shirt. Someone once gave me a Ronaldo Brazil shirt as a gift. Oddly enough, I also got a Ronaldo Portugal shirt as a gift. I don't even particularly like the Ronaldos*. I wore these shirts occasionally when playing football.
I just don't get it. I mean, I was up for Iraq against the US and all, but that doesn't mean I was going to buy a National Guard uniform.
I can understand casual fandom: I like watching Spain at the moment; I've long been a Zizou fan, and would watch France for that reason; Heck, some of the better Italian teams have played beautiful defensive football. That didn't make me a fan of any of them. Fandom requires an emotional connection. If you don't have close personal ties to a country, claiming to be a fan of their NT strikes me as a shallow fandom - false associations forged out of some meaningless need to be part of something successful. At least non-Turin Juve fans (and non-local club team fans in general) track their team for most of the year. NTs play so few games that it's just not enough time to actually connect with them. It's fake.
*No, that is not ironic. If you even thought that, you don't know what ironic means. If you didn't think it, you also probably don't know what ironic means.