My understanding as to what makes certain Louie plugs much more valuable than others falls into two separate streams.
The first stream is that of the true collectors. They are looking for rare models including early wood plugs in rare colors etc. Original condition is critical to high value with value being related to being in mint or as close to mint condition as possible including having the original packaging/box. There were a great many Louie plugs made over the years but very few with the Shovel nose and the company that made them has been out of business for some time.
The second stream is that of what I think of as the highly sought after plugs to actually be fished, specifically in the Campbell River Tyee Club row boat fishery in the Tyee Pool. One of my brothers rows in the Pool and he is always looking for undiscovered true Louie Shovel Nose plugs. The club rowers want the true Shovel Nose Louie plug because that design gives the plug a great action for enticing the non feeding terminal fishery Tyee and does so at the very low speeds that the rowers are able to provide to give action to the plug. The non-shovel nose Louie plugs cannot be rowed fast enough to make them nearly as effective.
My impression is that many factors go into how much one of these plugs will sell for and pedigree or provenance of the plug can play a big factor, even more so than original condition of the plugs. Sometime these plugs can be modified such as being repainted in modern or glow paint etc without hurting the value of the plug. What seems to effect value is the plugs history. Has it been previously owned by one of the historical Legendary club rowers. Has it been owned by one of the current top rod rowers and used to recently win a top guide/ largest fish for the year award etc. In its history of being fished in the pool, how many Tyee has that plug caught and been registered in the club book? I suspect that there are some minor differences between plugs that may account for some plugs being more successful than others but the skill and the experience of the rower/guide is likely the big factor.
A lot of what people may be willing to pay for an old well used lucky Louie Shovel Nose plug is psychological. Owning one that is covered in Tyee teeth marks and formally owned by a legendary Tyee Club guide and is known to have put a lot of very large Tyee into the club record book is likely going to be in demand. Perhaps some are hoping the luck and the spirit of that plug will rub off on them and help them put a 50lber into their row boat and into the club record book. Perhaps in a small way, it is a little like owning the well used guitar of a famous rock star that was used in a number of legendary concerts.