Hello, my first post here.
Personally, I don't buy into the frequent replacement thing. I just recently changed my sand wedge from an old Ping Eye2 56 degree that I bought used for $20 to a new Cleveland 588 54 degree. The Ping is out of the bag and the loft change took some getting used to, but other than that, both clubs perform exceptionally well for me. This despite the fact that one is more than 20 years old and the other brand new with the buzz marketed Rotex groove thing. I'd say if you are happy with the wedges you're playing, no reason not to hang on to them. I bought the Cleveland because I pretty much bought into the groove hype, but my average score hasn't noticeably wavered at all. I can't justify dropping an additional $250 for a new set of wedges every season with numbers like that. I'd rather spend the dough on green fees, practice balls or lessons.
First, welcome to the site! I see what you are saying and agree for the most part. However, for someone who practices and plays a lot like myself I will notice a change in how my most used wedge plays by the end of the season. I will notice the ball start to roll out a bit more on certain shots closer to the green where I would get it to spin and stop before. For me it is probably changing out just the one I use and practice short game(and sand shots) with all the time and then changing the other wedges out every 2-3 years.