No one ever made a profit by investing in a personal airplane. (or even broke even - and as a plane owner for over 50 years I can prove it)
The market value of the plane is exactly what the buyer and the seller arrive at (shrug).
'Wait for next year', they cry. If it is a nice plane, it likely won't be there next year - and if it is, who says the seller will accept even one penny less than right now?
Having said the above:
Now for stocks, I would wait a year - give or take. I expect a correction in the market. But, owning a stock is a vastly different decision than an airplane and made for vastly different reasons...
For farm land I am waiting a year or two. When the market corrects, a fair sized chunk of the money currently parked in farm land for safe keeping will be pulled out to grab up cheap stocks. I will be there to pick up some cheap(er) farm land.
There are dividend paying stocks out there with long track records and returning 3.5% to 4% (my holdings return 4.1%) If you have or can rustle up a $100K for dividend yielding stocks in place of an airplane you will have $4,000 a year coming in. That will pay for a chunk of a 100 hours of annual flying time from the local FBO. Just sayin'....