The idea of cues (certain cues to be sure) only going up in value is speculation, especially when you look at it in relative terms and compared to other alternatives. I invest a portion of my portfolio in gold for two reasons, one it is a good hedge against inflation and two, it traditionally has some
negative correlation the stock market. But like gold, cues to don't pay interest, earn money, or have any ability to be valued based on anything other than what a buyer is willing to pay at the exact moment the seller wishes to sell.
I would be a cue collector and not an investor. I would collect the cues I want to own without thought to future value. Take Gus or bushkas, how much have they increased over the last 30 years. A ton! The greater the previous return, the less growth you should expect moving forward. To wit, add inflationary adjustments less an expected alternative ROI from other hard assets, I would take my chances elsewhere, especially since other hard assets can be leveraged. Not really feasible with cues.
I don't know if this helps anyone but, just like my other more expensive hobby- wine, I collect (and drink) but have assigned myself to not approach it as an investment or a way to make money.