Full systems were made by: Akrapovic, leo vince, micron, hindle, jardine, tsukigi, arrow, and probably a few others that I am missing, and of course yoshimura. You can still find them from most of those on that list, but try and find a yosh full system and it wont happen. Don't really see why that is relevant. You seem to feel the need to bring that up all the time like they did something special for the RC51 community, while they just did what most of the other major manufacturers did.
From my admittedly small experience, the yoshi pipes are not at the same level. The welds aren't as clean on the mids and end caps (which are dog-shit ugly). The carbon cans feel like a boat anchor compared to the akra and leo cans I've held recently. Never weighed them, but the yoshi cans are definitely heavy. They feel like they weigh almost as much as the stock bits. I don't know how or why, but they are f-ing heavy.
One of the more tangible reasons with the akra's and sato's are a better product and cost more is the fact that they have titanium mid-pipes, and yoshi's have stainless steel. Some also have Titanium end caps and some are also all titanium construction. All that costs money, and some feel the need to have it, and some don't. Different strokes for..... It's all opinion man. Some people drive a chevy impala, some drive a bmw 530. Both will get you there, but are made differently, look differently, and perform differently. Is it worth it? That's up to the buyer. For me, all it takes in one look a a yosh can and mid next to an akra or leo, and I know which I would like to run. The leo's which I currently have, I am not overly impressed with but they are still better quality than yoshi.
It's the same argument that was being hashed out over carrozerria (sp?) wheels. They may cost less than others, they may be light, but some like them and some don't. Personally, I don't like the way they look that much, and they aren't that much cheaper to justify throwing my ass (and cash) on the line with all the bad things I've heard about them. Is it worth it for the extra cash spent on another brand that I think looks better? Well if that is up to me, yes it is. I haven't had any personal experience with their wheels, so you wont hear me call them pieces of crap, but if someone asked me for an opinion, I would tell them what I have heard and that they should do some research and see what they find.