I simply disagree, I don't believe that ferrule loosening is something inherent to spey rods. I've seen dozens of single handed rods broken for the same exact reason. It's caused from whipping the rod without a good load on it. I believe that most of the people that tape their rods never even had a problem with their rods loosening, they just tape them because that's what they heard they were supposed to do. I've seen a lot of spey rods broken too. Almost always (in both cases, single and double) the rods were broken by someone very new to fly casting and wasn't quite getting it yet, and then hooked a salmon. That's not to say that taping is for beginners, most people seem to do well enough to keep their ferrules together (nobody tapes single handers). If your someone who started taping because you had a problem with your ferrules loosening, I'ld bet (figuratively) if you tried fishing without it now, that you won't have a problem.
I also think that checking your ferrules occasionally is probably just as easy as taping them. I have, and use, a variety of brand name spey rods and Ive never taped a single one. I've also never broken one at a ferrule (heres to hoping that I didn't just jinx myself). But I have noticed a difference (between brands) on how often they tend to loosen up a bit, particularly in the summer.
A bit of parafin wax can keep ferules in good working order.
I know quite a few very experienced spey rodders that don't tape their rods and share my opinions. I'm new to the chatroom experience but I'm not new to spey casting. I do agree about the incredible performance of a spey rod cast. I really don't mean to be argumenative, I'm just sharing my take.