My thoughts
-While finding domains with potential end users requires some work, it is far more difficult to find buyers willing to open their wallets. When you are dealing with TLDs other than .COM you exponentially increase the amount of marketing effort or patience (renewals for X years) to receive inquiries.
-It has been rare for me to sell a domain a short time after acquiring it. Normally sales occur years later even for .COM domains.
-While very short .COM domains are in demand, I believe with so many other domainers mining that space, finding bargains in LL or LLL or LLLL .COM will not be easy. While the new TLD mania has cannibalized domainer to domainer sales, one positive effect is there is less competition for expiring .COM domains than would otherwise be the case.
-I personally believe the new TLD and numeric domain bubble will burst in the next three years. There is far more inventory being added than there are end users and unlike baseball cards or coins or collectibles, holding a portfolio of domains entails a carrying cost. In many cases domainers are registering hundreds of domains with a teaser reg fee of $1 but a year from now when the renewal is $10, how many of those domains will get renewed? Or in some cases they hold premium domains with renewals of $50 to even hundreds annually. With numerics, why would a business brand their company's product / service offering on 74832910.xyz or 64071825.ws? Are those names memorable to customers? So why are domainers buying this %^&*$#@!
-The biggest challenge this industry still faces even in .COM is the mindset of end users toward domain names. Generally speaking they merely look at domains as low $XX costs necessary to launch a website and give little consideration to the branding aspect of the selection process. They will then proceed to spend five or six figures on website development and marketing costs on a poor-quality domain. Until that end user mindset changes, I do not see how the mushrooming growth of new TLD registrations can be sustained. There are not enough end users buying domains to maintain a portfolio of such names.