Uncle Jimbo's Get Mediaeval
|"Downward and onward!"|
Lightsaber Special Abilities
Maybe a lightsaber could acquire one of the following abilities if the maker spent additional Force Points above the one point required. Each additional Force Point would also provide a bonus to one of the required ability checks as normal.
The weapon could add 1-point Force bonuses to other things than To Hit or Damage when a Jedi's lightsaber is in hand and ignited, based on the skill-enhancing Force feats that he had at the time of constructing it. For example:
Attuned: +1 to DEX or STR, chosen at the time of construction
Some of these feats are clearly more related to combat than others. Apart from Mettle, these bonuses should only apply to the Jedi who constructed the lightsaber.
Another possibility is a weapon with special purpose that takes on an ability based on the place and circumstances of its creation. For example, Luke constructed a lightsaber from Obi-wan Kenobi's journal at a time when his destiny was guided towards facing Vader and the Emperor to preserve the Jedi order. It could take on some aspects of a target bonus, based on Obi-wan's Jedi Investigator abilities.
In fact, it's quite possible that two special-purpose weapons clashed in the fight in the Emperor's throne room, since Vader's red saber seemed particularly effective at killing Jedi.
Darth Vader's lightsaber would have been constructed at some point in his advancement as Sith Lord. Thus, if it has a special purpose ability, it should be related to his listed Sith Lord abilities. It would make best sense (based on the fights in the movies where he uses this weapon) to give him something based on Rage, say a +2 Force bonus to Strength when the lightsaber is used to attack a Jedi.