I agree with both of your comments. NNN and LLL are valuable both due to 1) Easy memorability 2) relative Rarity 3) Many acronyms 4) Very Brandable
Only 1000 NNN and 17,576 LLL can ever exist in any extension.
This may seem like a lot but over 50 million domains are registered but how many are short and sweet like NNN and LLL?
As investments LLL and NNN names hold a nice balance between value and growth. They will rarely be the biggest and most valuable names but they will steadily appreciate in value.