Well, I bought MK4's 20 years ago as part of a development effort that lead to the original RBox design which led to the NBox. If I amortize the cost it is under $20 per show which is quite reasonable. I have not felt an overwhelming desire to upgrade except possibly another pair of capsules. I just purchased a set of ca-14's for my 12 year old son as a starter rig. There is a noticable difference between recordings but not 10X better. In my opinion I'd say stick with what you have unless you are going to really go for it. Otherwise you will still have the urge to upgrade but you will have a second set of mics to sell and potentially take a loss on. Again, just my opinion.