One of the things that has bugged me in WotLK (and probably happened in other expansions too), is that flasks/potions ect. do not scale. The common caster flask, Frost Wyrm, for example, always gives a flat +125 spellpower.
At the start of WotLK, just entering naxx, most people had around 2000 spellpower, more or less. 125 added to this is an extra 6.25%, a sizeable amount.
But, now at the end of the expansion, high end players have mostly over 4000 spellpower if they stack it. this dilutes a flasks value to only 3.125% of their spellpower, a much smaller relative dps gain.
I would love to see flasks which had effects such as "Increases your spellpower by 5%" or "Increases your attack power by 8%".
This would make sure that flasks are equally as valuble no matter what your gear is.
Obviously, flat percentage increases scale very well between expansions so restrictions would have to be used. Perhaps put a level 81 requirement so that it cannot be used in WotLK raids (I guess people will make WotLK guilds like they do BC guilds today), and make it unusable, or have a reduced (say, half) effect on players level 86 or higher, for when the new expansion comes.