I suggested this thread on the L&L one as I think this is a really important question and so have voted other.
Like most things with D&D, I prefer to have the fiction first and meld the mechanics around that fiction. The touchstones I would like wands to hit are:
• A wand is highly personal to the wizard. The wizard crafts it or has a wandmaster or master artificer specifically craft it for them. A wand should say something about it's owner.
• Using a wand as against an orb, tome, staff or other implement is a core decision a magic-user makes. I would suggest that a wand-user focuses on spellcasting as against rituals, sorceries, alchemy or other fields of the arcane.
• I don't want wizards to have a golfbag of wands. A wizard should bond to a specific wand as against other arcane equipment or possibly even a familiar.
• A wand might focus on a particular field of spells such as fire or shadows and assist the caster in being more effective in that focus area. A wand might have one or possibly more spells impressed into it that can be cast through the wand using a spare vancian spell slot that the wizard may leave open.
• Continuing with that wand theme, a wand might give access to a particular spell that cannot be cast except through that wand; it simply cannot be cast or brought into effect otherwise.
• And perhaps most importantly, different wands should be different rather than all of them following the same template. Perhaps some could store magical energy (although that feels more something that a staff or orb should do) while others might assist casting in general (making the caster level higher if such a thing is part of the new ruleset). Others are highly focused around a theme while some might improve the flexibility of the wand-user while others might assist with ranged touch attack spells. [The hidden aim here is to push the caster in a particular arcane direction rather than being good at everything.]
The thing I do know is that a wand as spell storage is not consistent with many of the above; so I'm firmly in the implement camp but with extra diverse stuff thrown in (that could include a smattering of spell storage).
Best Regards
Herremann the Wise