Ahh, yes. I still don't know exactly how I'm supposed to get the Mirror Shield, but when I first played through the game I missed my chance to get the Light Arrows, so I had to start over and play through it again to get it...
The Mirror Shield sounds pretty useless. All it does is reflect magic attacks, and that has barely any use even if you were to acquire it at the beginning. At the end it's... useless. I haven't actually gotten it, mind you, but I don't really see it being any other way.
The Light Arrows were odd in that there was a point where they could no longer be acquired. I actually hated that. Never in the history of Zelda has that happened. I blame it on Capcom doing the game. Anyway, aside from that, I had no problem with them. They were a cool addition, little charge-up arrows, and I found them quite useful, especially against the Gibdos in the Palace of Winds and Dark Hyrule Castle.
And the Magic Boomerang? I loved that thing. Sure it was a bit of a pain to collect, but all you needed to do was find all the Tingle brothers. It wasn't that bad. And it was a great item. Not only did it have twice as much reach, but it could be controlled mid-flight, which was cool because it more closely resembled the Boomerang in the 3D Zeldas (and that's one thing I loved about Minish Cap, how it was a 2D Zelda incorporating many elements of the 3D games).
I always like, in Zelda, having special optional items or upgrades, so I enjoyed these. It was a little disappointing at times how few opportunities you got to use them, but that's really my only problem with it. I can understand complaints about the Mirror Shield though. That's... kinda lame... -.-