I dont have too much to say on the whole wearing Gi to the dojo hting, I dont think it is much of an issue. Unless you really feel the need to judge someone over somethining like this for your own sake.
but, I studied japanese for a little while, and my tutor told us many times that if non japanese follow japanese customs very closely, or understand them very well then they are considered strange. I cant remember the name that they use for people who do understand but it is something along the lines of 'strange foreigner'.
So it is a little difficult to insult the japanese by not stricly following their customs, as we are not expected too. and I guess this is what it is all about, etiquette. So wearing your Gi to class, even if not considered to be very good etiquette is not really going to cause anyone harm or major upset, so again it comes down to personal preference and personal disciplin.
"There is no spoon"
You're probably thinking of "hen na gaijin". Of course, foreigners are often considered strange no matter what they do :-). One of the pluses of this is that foreigners in Japan can often escape some of the normal societal requirements if they want to.
I've lived and conducted business in Japan and in Japanese for a number of years, and Japanese people both expect and appreciate it when you follow Japanese customs, just like any other tight knit cultural group that you live among as an outsider. My hunch is that the kind of person that your Japanese tutor is talking about is the kind of person who attempts to be "more Japanese than the Japanese". For example, I know of a foreigner who lived in a restored 17th century farmhouse without electricity and cooked over a fire pit. He'd go on at length about how Japanese didn't understand their own culture - never mind that nobody in Japan has lived that way for several hundred years. It's sort of like moving to Alabama, instantly adopting a heavy southern accent and lecturing the local residents on how they've forgotten the ideals that made the south great. Not likely to be appreciated - just making a normal effort to follow the normal local customs is much more likely to get you accepted.