Do I keep a stack of random playfields just to have them? No.
Do I keep a few playfields for games I intend to restore and/or plan on soon acquiring? Sure.
Most of what I hang onto has an intended purpose.
But, I did speculate once on an extra CPR TAF playfield since past CPR playfields sold quickly for popular games and for a small profit after the run was done, but now the market seems to be flooded with them, so that didn't go according to how I thought it would.