I love Trader Joe's also, and I generally find both their prices and quality to be very good.
I don't buy very much canned food there, almost none, and the frozen items I buy are mainly bagged vegetable mixes, or vegetarian entrées I like or can't find elsewhere, or some dessert items. I am always finding new products and items I want to try, and generally my cooking becomes a little more inspired after a visit to TJ's.
I always leave the store with at least one bag full of goodies I had no intention of buying when I walked in, but which proved too irresistible to pass up--so the costs of a visit do mount up because I tend to splurge at TJ's much more than I do at the supermarket, but I consider it money well spent because the enjoyment factor is always quite high. For me, shopping at TJ's is just plain fun, and the reasonable prices permit me to indulge my tastes and my curiosity.
The only gripe I have ever had with Trader Joe's is that items I have loved and used for some time suddenly disappear from their shelves for one reason or another, never to re-appear again. This has happened with so many of my favorites that, when I head to TJ's for a specific item, I do so with a certain amount of trepidation that it will no longer be there or be available. I think a lot of that is due to the demands that TJ makes of its suppliers to try to keep costs down and sometimes that results in an item being dropped.
I know that's what happened with the absolutely decadently delicious Ultimate Chocolate Truffle Cake which was made for Trader Joe's by David Glass and which TJ's sold for a ridiculously low price of about $5.99 (which was something like $20 less than the same cake sold for elsewhere at places like Zabars in NYC and on Zabars web site). TJ's then tried to negotiate a price that would be less than what it cost Glass to make the cakes, and Glass just couldn't do it, but losing the TJ's account also helped to put David Glass out of business because TJ's accounted for 45% of the company's sales.
I really wish TJ's hadn't driven such a hard bargain on this particular item, which was, "Considered by many chocolate lovers to be the ultimate dessert" according to the New York Times, a view I would whole-heartedly second. It was just fabulous--pure chocolate perfection. And TJ's also carried a low fat version of the cake that was every bit as extraordinary and wonderful as the original. I don't know how many of those cakes I bought as gifts, but every recipient told me it was pure love at first bite.
I still feel a pang when I look into the dessert freezer case at TJ's because the Ultimate Chocolate Truffle Cake is nowhere to be seen. But, if it hadn't been for TJ's, my family and friends would probably never have been able to enjoy this sublime treat in the first place, or to have it as often as we did. So that helps to balance out the score. TJ's does carry many top-notch items I either can't find elsewhere, or I'd pay much more for if I could find them elsewhere.
I agree with you that Trader Joe's is not a store for everyone, and it's not a store I would even rely on for my everyday shopping. But what they do, they do very well, and it's a very pleasant and consistently interesting place to shop. There are two Trader Joe's each about 10 minutes from my house in different directions, and a third one about 20 minutes away, and all of them are always bustling, so business appears to be quite good.