Here's the way I see it, since you asked for opinions. Although I don't personally care for Dana Abbott, if I remember the conversation correctly Splice is not quite correct in his quotes. The first quote is definitely about Mr. Abbott (I'm the one that made the original statement). The subsequent quotes were actually referring to another fellow that is part of the same chanbara organization to which Mr. Abbott belongs. Bear in mind that I didn't bother to go back through the old e-budo thread and verify this, it's just from my sometimes less than stellar memory.
From what I have seen of Mr. Abbott's cutting and kata, I have been singularly unimpressed with his level of competence. What I've seen is sloppy and uncontrolled, which just shouldn't happen with someone of the stature to which he believes he is entitled. On the other hand, I've had many conversations with one of his senior students, who seems to be a very genuine and thoughtful individual. Therefore, I don't think that any seminar which Mr. Abbott may conduct would actually be detrimental, it's just a case of whether it's worth the price being charged.
As far as his skills in chanbara, I've no idea as it is a totally seperate entity and has no real bearing on Japanese sword arts in my experience. I have both done and watched chanbara and, despite what many people try to insist, it really doesn't have much in common with actual sword arts. Loads of fun actually, but I wasn't very good at it since my training actually worked against me when doing chanbara.