The Stevens Favorites are very collectible, if in good condition, and certainly worth saving. If you have shootable .25 rimfire ammunition, that also is worth money to those who own .25 rimfire arms. If you have partial boxes of such ammunition, and the Favorite is in shootable condition, you should shoot a few rounds, at least. It is not possible to safely convert the Favorite to .22 Hornet - the action is simply not strong enough. You could convert it to .22 LR, but a collector would likely trade you a .22 Favorite in equal condition for your .25, particularly if you have good ammunition for it.
PRD1 - mhb - MIke