Many years ago I was playing in a band when the guitarist had a mind-blowing new thing. The small stone phaser. It was an effect-pedal you could connect between a guitar and amplifier. Switch it off and on by stepping on its footswitch and watch the mouth of a guitarist when using an effect. So of cause I also wanted a phaser but, as an electronics engineer I wanted to build it myself. Cheaper and better. When opening the original I found a number of IC's with its type numbers removed. Still I was able to reproduce the schematic because It was a not so complicated circuit on a single-sided pcb. The mysterious IC's I recognised as being from RCA from the look of their housing. The 1974 yellow RCA linear data-book listed only a few 8 pin IC's with corresponding connections, so I quickly found it had to be the CA3094, operational transconductance amplifier. I designed my own pcb and built my own phaser with success and soon got requests for building more of these for other musicians. Only then I found that copying such a device was time consuming and expensive because I only calculated for the components and a little extra but forgot the enclosure, batteries and the time it took to build one. So I never built another. However, since then I found it a sport to demistificate all kind of hidden electronics. A publication from an author, stating "selbstbau lohnt nicht mehr" while showing the schematic of an amplifier, developed by Ottala and Lostroh for Philips, and hiding part of the circuit in a potted module you had to buy from him. Even nowadays one can find apparatus with sanded type numbers of components while the cynical is; this is now mostly done in circuits not to prevent the circuit being copied but to prevent someone finding out it is a copy.
At the same time I find that manufacturers who do spend a lot of time and effort in developing new apparatus, often make the schematics of their products available for downloading on the internet.
So what do we learn from all this.
First I think, there is more to a good product than it's price only. There is the quality of built, reliability, long term availability and service that do count. Protecting your products from being copied is better done by making use of programmable devices, used in such a way that they control or handle a substantial part of the device they are used in.
Another way is making use of multilayer pcb's that hide most of the circuit lay-out in the inner layers,
Now what circuits are critical for being copied ? First thought is "all" however, it is mainly consumer electronics which often conflicts with using multilayer pcb's or FPGA's due to their relative high prices.
So the next factor in calculating is the loss when a copy of your product will enter the market and turn your profit to near zero.