The answer is everything!
Just joking a bit........buy seriously, I think the answer is diversification. If you toss all your eggs (literally) in one basket....you could come out on the short end of the stick.
Co-Doms/Doms are popular because the return on investment happens in the first generation. However, as you indicated, their value will drop much more rapidly then Recessives.
If it was me and I had 18K to spend and that was all I had. I would not spend it on one hot codom. I would get several solid snake mutations that down the road I could cross for new combinations. More morphs in your bag of tricks opens new options for your breeding group. When you stop and think about it, you can generate a long list of combos that have not yet been proven.
I like the idea of some recessive and some codom/Dom in my collection and then begin crossing them. Then you get pastels het for whatever, spider hets, mojave hets.....etc in the first generation. What will sustain the value of codom/dom is combining them with recessive animals.
Also, get a codom/Dom that is extremely diverse. The pastel is an excellent choice. Everything can go through this codom and get brighter with more blushing.....an then there is another level still with the super. spiders are on fire....but I still see the greatest long term investment being the pastel. Spiders to my knowledge do not! have a super.....they are dominent. Yes yes yes.....I do realize the verdict is out on this a still. However, there has been many spider X spider breedings........and I have seen zero supers. If someone has a super spider please post it.
A pastel male is an automatic...make sure you have an army of adult females to go with him. I think this with one nice codom line makes for a deadly combo. If you can afford more of both...then get them.
Jim Perron
Python Passion