An old man told me years ago "That sounds like a great idea, build a $100,000 Barn to protect your $100,000 worth of equipment"
I think the old man was wrong . . .
As you say, you can always downsize. Chances are you WILL fill it up, sooner or later.
Your $100,000 worth of equipment will last longer, take less maintenance, keep its value better and work better if it isn't left out in the elements and is protected from theft, vandalism, joyriders, critters, you name it. Remember, your equipment was bought to WORK, it wasn't bought because it was a trophy of some kind. If it won't work, you are losing money.
In 20 years, the value of the equipment inside the barn could easily be $200,000 or more, the barn is still $100,000.
If it is part of a business (farming, used for business purposes, etc.) you can deduct any interest payments on the mortgage and you can also depreciate it. Don't forget expenses - maintenance, power, and so forth.
When you go to sell, it will appraise (assuming it has been kept in good condition) at current replacement cost or close to it, which is going to be WAY more than you paid for it 20 years ago. (Exception - I am given to understand that in farms, the value is in the land which makes income and structures on it are not as important in the valuation.)
You will also have had the utility value of it for all the time you owned it. Mini-storage is atrociously expensive and there is a national shortage of warehouse space.
Size matters, bigger is better.
Best Regards,
Mike/Florida