The hat is cute, and could easily be fitted to 17" Duffy with a bit of elastic and minimal sewing. The shirt is just the typical US click-n-fill "design," so no loss there. It was cool when they had the T-shirts for each park for the full-sized Duffys; do they even still make those, or is it all "Disney Parks" now? I was impressed with those because they were something we don't have in Tokyo that actually seemed like something American Disney tourists were likely to genuinely enjoy. It's a very American concept (Japanese Disney fashion is quite different), and it seemed like a sincere, natural and memorable item that might actually enhance someone's connection to Duffy. That's my measure.
NOTE: Looked it up and they still exist. I could only find the WDW one on the website, but there was a different one for DCA. Well, it had a different print, at least. It's exactly the same colors and base design. I really thought these were different colors originally, too... Still, I like this. It's not something I would ever buy personally, but I can imagine that US park-goers might actually find it charming. If it was $10 or under, I'd also think it was somewhat reasonably priced. It's $18, though, which I consider highway robbery.
This Tampa Bay Rays shirt (hey, Aimster!^^) from Build-A-Bear goes for $6.50, but it doesn't include a hat. Still, it also has a more complex neckline and looks to be made from higher quality material:
This one is more directly comparable to the Disney one, though still with a far nicer neckline, and it sells for just $5, as do most of the other Raglan tees from BAB, except the ones that are $6.50...and the ones that are only $3:
My advice would be to buy an iron-on and a blank BAB raglan tee
(also $5), and make it yourself. Or even make your own image, print out your own iron-on and have a super custom job just the way you want it.^^
Tokyo items cost more than the US, no doubt. But when it comes to value for money and not feeling like a chump, I'm far more impressed with OLC and BAB. You're probably right that some Tokyo fans also think the US stuff is cute, but I've never seen it in the parks. I've seen it for sale on auctions and websites and even in shops, but I've never seen anyone actually showing it off. Disney is not invested in doing this well and their prices are a total rip-off, speaking bluntly. They make Duffy look like a scam, and he's not!