No matter what you do, there isn’t room for an infinite amount of useful items. Even if you make more uniques playable at endgame, most uniques will always remain worthless. I’ll add that most uniques and set items are common enough that even if they become viable for endgame they’ll still remain worthless.
Not to say there isn’t room for buffing some of the uniques (Community Feedback for Improving Itemization is a good place to debate possible unique buffs if the devs ever decide to buff them), but I’m not sure what you are expecting to achieve. I’ll also warn against power creep, as making uniques more competitive is likely to overall increase top power.