Speaking as someone with too many camera systems ... The F2 and F3 are compatible and relatively similar in operation. Keep both and one is the backup for the other. If you need to dispose of something for simplicity or to make room, get rid of something else that isn't compatible whose niche can generally be filled by the F2/F3 (eg some other manual focus SLR).
I feel like the get-rid-of equation is different when these are ~ $200 bodies vs being ~$500-1000 each . That is, if you had too many of some really pricey thing, it makes sense to sell one off. But if you have too many of some moderately priced thing, and you sell one, then if you ever want it again you spend X amount of your time finding it, and how much is that time worth?
I feel like the get-rid-of equation is different when these are ~ $200 bodies vs being ~$500-1000 each . That is, if you had too many of some really pricey thing, it makes sense to sell one off. But if you have too many of some moderately priced thing, and you sell one, then if you ever want it again you spend X amount of your time finding it, and how much is that time worth?