Few cues if any hold value like commodities. Production stuff will only be as valuable as the demand/supply requires. As you and others have noted, pool may be waning at this time...and that will affect the "equipment" used to play the game. I wouldn't invest in Predator shafts for full retail expecting them to pay back dividends later...
But highly collectable cues are not necessarily linked to how many players are in the sport, or how well massive cue producers are doing financially. To predict custom (investment grade) cue trends, one must look to other indicators for signs of investment quality. Factors that will affect cue availability, name recognition of a given maker and rarity of materials used are all important considerations.
Joel Hercek, Barry Szamboti, Dennis Searing, Ron Haley...these builders have such a strong following and are so careful to execute top quality no matter how this reduces their output of product, their market will be stable for years to come...there is also the possibility of big surges in demand should any one of them choose to stop building cues for any reason...those are investment cues.
Southwest cues have had a consistent track record of high demand and the cost of such cues is well understood. To escape the 10+ year wait, most are willing to pay a premium. While these cues are not going to make anyone a big profit, they are more stable investments. If you want profit, selling a place on the waiting list may be more lucrative than selling the cue after you get it...but in either case, you will not take a loss.
Cues like those of Mike Cochran or Art Cantando are highly limited in availability and will likely always be prized. Acquaint yourself with the correct collector values then compare them to the asking price of the cue and you can make a sound investment. Buy on a name alone, however, and you could own the right cue for the wrong money and never profit...
I suspect cue collecting of fine artistic or rare collectable cues will be a solid means of owning special cues, then selling them for the initial investment or more for a long time to come, but cues are not and have not been a means to easy money for anyone in a long time.
Be clever and buy right or pay for the education with investment losses as you go. It is not for everyone, but I have no regrets for the many thousand I have spent following this passion.