I get that you are just talking in generalities here, but I am curious as to what you consider to be "huge amounts" so as to warrant a hardware wallet and how you came up with the sub $500 in value suitable for a more economical mobile wallet (with the supposed implication that the higher security hardware wallet is not really necessary for anything below $500).
$500 was just sort of a rough guess, so don't over-interpret that 
. Deciding when getting a hardware wallet is "worth it" really depends on the holder.I'm going to guess your rationale is probably based on the cost of a Trezor or Ledger itself... If you only have $500 in BTC value - why would you spend roughly 20% of that on a more secure wallet when there are any other less expensive options out there? Seems a bit expensive!
True! Though that's assuming that the person using the hardware wallet would not add more bitcoin/crypto to his/her wallet. But yea, if it's only $500 without any plans of adding more coins/tokens, then definitely not worth it. Again, hugely depends on the intentions of the holder.