Magical item bonuses - House rules

Binding magical items to characters is a complicated matter. The latter tends to pick new items through adventuring and discarding irrelevant equipment.
The following set of rules was created to enhance both the gameplay and the way characters (and players) feel towards their "collectibles".

Imbuing a weapon or a piece of armor with magical energy gives out a flat +1 bonus to the item. These items are mundane and usually discarded once a better piece of equipment is found, but what about +1 Keen swords ?
Should they be discarded as well?
For the purpose of crafting the item, it is treated as a +3 item.
In the new set of house rules, these sort of weapons (and armor sets) can be utilized with better efficiency as the character gains more levels up to the maximum of added bonuses from weapon properties using the following calculation:

• Up to level 8, +1
• For each four levels above 8, the item is treated with an additional +1 if enough properties are set on the item, thus a level 14 character wielding a +1 Keen dagger treats the weapon as if it's a +3 Keen dagger. At level 16 the item must be enhanced with additional properties in order to gain an additional +1.

Through these simple rules, characters gets to keep using their equipment, often attaching emotional and historical meanings.