How to make mage robes a viable alternative to armour?

So, like many people, I don't like the artificial restriction of no armour use for mages. I never found any explanation why clerics can cast in full armour while it somehow stops arcane magic. I also recognize however the need for that restriction for game balance reasons and view mods which remove them altogether as cheat/exploits that make mages and F/M even more OP. Mods which add casting time penalties and/or miscast probabilities serve only to slightly reduce these problems, by what I see as another arbitrary, unexplained mechanic.

Another gripe is that somehow in Forgotten Realms there are wizardy robes and braces giving protection equivalent to best traditional armour - another example of fixing a broken feature by another broken feature.

So, how to make mage robes a valid choice if we allow mages to use armour? By making them better in other things, more helpful to mages. Frankly, all the standard issue robes are kind of crap anyway. The big question is how to make them good without being overpowered on already the most powerful class?

Mages are are rather weak early game - fragile, with only a couple of spell slots, no good with any weapons. So I think we could safely give them a boost there even with common robes:
1) Higher elemental resistance; not simply 15% to a single one, but to all elemental damage;
2) Additional low level spell slots (for example, +1 on levels 1-4 on unlock of the level.;
3) +1 to saving throws
4) haste (not much use on a caster, but could help escape tough spots)
5) a couple of invis casts per day
6) 1 Im. Invis. cast per day

Rare stuff could give:
1) -1 to casting time
2) +1 to casting level
3) 10-30% magic resistance (depending on the point of the game)
4) saving throw penalty to targets
5) Invul to paralysis/petrification/vocalize + free action (depending on the point in the game)
6) permament 'true' blurr
7) permament lower level 'mage armour' or shield spells (or just a couple castings of those)
8) 'blessed' robes granting use of some divine spells
9) All sort of 'once per day' affects granting higher level spell casts. The wands which offer Breach/Pierce Magic/Dispell are already quite common and it would make quite a bit of sense for them to be available on the robes

Basically, anything that can be found on a wand or a ring might have a slightly more powerful form in a robe. Nothing stops the players from juggling the rings once their ability is used up, so I am thinking only in the lines of a convenience tweak rather than something clearly better than was available.

As a side effect, bards being able to cast in armour, also get a much needed boost (and why not allow them the use of robes?)

Thoughts?