I'm a little on the fence over which circumstances I buy mutated/unmutated dinosaurs. For example my boss rexes, the ones i have currently probably have over 350 mutations on each side, but I only use them for one purpose - to farm boss runs. I don't see them as dinosaurs I breed to optimise, since they perform the task they already do suitably.
Farming dinosaurs - quetzals, therizino, mammoths, giga, doedicurus, ankys etc - the better stats I can acquire, the quicker I can perform medial tasks such as farming resources, whether it is meat or stone/wood, the quicker i can return to playing the game. So another circumstance I wouldn't be too bothered about mutations and try to gain when I can.
For me personally, un-mutated dinosaurs increase my end product potential. If I can get as high stats as possible without mutations, thus allowing me to offer a better end product - I can then either breed repeatedly to hopefully fill a gap in the market (for example having the highest stat on a dinosaur on the market) or can offer clean lines to customers. From my experiences, little or no mutations definitely makes a sale more encouraging to the buyer.
Then there is dinosaurs I class as my "Interests, or hobbies". Every breeder probably has a few breeding lines they take priority with or often hunt for their best stats available for and actively search out improvements.
Yes there is some dino stats I wouldn't sell, but this is mainly since I have seen reluctance from other sellers in situations to share their own. I keep these dinosaurs aside as "Leverage" in a way, to offer tricky or difficult traders into making a deal. By keeping my rarer mutations more exclusive, it definitely will help secure a deal on my end.
However - i'm not too sure if people are more willing to trade stats etc, if that would be a possible solution for the tame cap. There is a large difference in opinion of the value of certain dinosaurs/stats and I feel bridging it between some traders on the forum might be too difficult an obstacle to overcome for it to be viable. I have always tried to price my dinosaurs on the lower end of the pricing range - encouraging myself to sell "many eggs/dinos at a lower price" than "fewer at a higher price". Which hopefully has given buyers the potential to step into the trading market and create a foothold. However I often see trading posts where players are selling similar or the same dinosaurs for a higher premium.