So I was thinking about some stuff I've heard over the years, like original skirmish/chainmail/proto-dnd terminology coming from d6 based systems?  Like.. +1 magic weapons doing +1 to a d6, making +1 actually be a very good 16.6% bonus,  compared to +1 on d20 being just a 5% bonus.

This got me thinking about setting a minimum floor bonus of +3 for all magical weapons, maybe +4.  This would make all magic weapons significant, and probably would be handed out less frequently.  I got to thinking that other bonuses/powers and abilities attached to different weapons would be a good way to differentiate them rather than having better/worse to hit bonuses as being something that is ALSO used to differentiate them.

So I dunno, a good idea to pursue? I like the example of the holy avenger, where it gives extra stuff to the paladin, so I was thinking on making a series of weapons similar to that, which give a certain bonus to specific classes, and then other weapons which have bonuses for any character,  weapons that allow spells to be cast by classes which don't get to cast spells, things like that.

This is very similar to the way Dolmenwood does it. All magic weapons are +2, and then there are rollable tables for special qualities. I certainly get the logic. It's a nice way of avoiding the situation where you throw away your extra special magical sword you got from the knight's tomb because you got a +3 one from a random troll horde. I'd just say be careful that your AC and HP numbers are set up to account for it, as a lot of games assume that magic item progression in their leveling tables.

Rather than items that are specific to classes, I'd be in favor of items tailored to certain types of opponents, at least if you use random loot. Picking up class specific weapon is going to be a bummer if you don't have that class in your group. But in general I think the best magic item effects have more general utility. To use an example from Dolmenwood, a weapon that can shrink to the size of a keychain is potentially useful for anyone. I also like magic weapons with non-combat properties. For some reason I think of the sword in Thundercats, that lets you communicate with your allies and have limited clairvoyance.

I use a system where magic items are rated by power level and have a duration. So magic can fade from an item unless more is infused into it from a temple or wizard's tower. Then an item system that provides a quality level. End result is typically runs -2 to +3 for mundane quality and +1 to +3 for magic power enhancement. The magic bonus will drop to 0 for exhausted non permanent enchantment. Since I find +magic to be boring, I try to add details to all magic items. Think Sting from the hobbit. Probably +1 and glows in the presence of orcs.

This is a magic sword I made for a character in his quest to free his ancestors from a curse of being bound to the grave because of their failures in a previous age.

Sword of Chaos Smiting+1 to hit and damage. Vs Chaos creature +1 damage per creature HD. 20' protection from chaos mind effects when displayed. On a special success, chaos creatures must make morale roll or flee. Medium/Solar. Recharge 2d100+40 SP.

Medium/Solar refers to it being a medium power magic item that is powered for a solar year. We us a silver economy. Refreshing it's magic costs him 2d100+40 SP per year.

Remove feats from characters and give them to Magic Items to make them unique.
A feat can only be used by one magic item to make them unique.
Dump the +1/+2 entirely.

Hmmm yeah, the system I'm working on doesn't have feats, I was thinking magic items would be the "progress" and provide majority of the specialization that characters have.

Well that's the point, if you don't use feats the players aren't as familiar with them and if a feat is overpowered you can have something happen to the weapon (must drop it into Mount Doom, etc).