It depends on what you define "hard core" as.
If one out of every 313 people were tool collectors in the USA, then there are one million of us. (1/3 of 1% only) (US population is ~313 million.) If there is one hard core collecter per thousand regular collectors, there would be 1,000 hard core collectors. I spend 6 or 7 thousand on tools every year 75% new, 25% vintage I would think. It's easy when hammers cost $46 to $115, and stakes not much less up to considerably more than hammers. I am not even hard core by my definition of the word, I am a user collector (but I can afford a lot of higher quality tools, even redundant tools or specialized tools) BTW - I do not use anything mire than office tools to make my living for the last 27 years.
I've seen more than 50 or 60 "hard core" collectors. I am sure there are more tool collecters, or those that want to be, than stamp collectors (a dying group.) If you measure by collection value (or amount of product in collections) I think tools is up there, primarily because tools cost a lot. Most car collectors have a collection of vintage tools also. Gas pumps are hard to get ahold of, and they were on every corner.
Stamp collecting is suffering. Millions bought sheets of stamps, expecting them to increase in value. So much is out there that you can buy stamos printed since the 1930's for 50% - 30% of face value. They are still legal to use as postage, or to pay for postage. Philately peaked sometime in the 1940's. They actually lost a ton in value.
Generally speaking I think used tools hold their value. New tools lose value when first bought, generally. If you put forth a modest effort I think you can buy used tools well below their future resale value.
Chilly