"The reason for this post is that I feel that some uses of haste are unbalanced."
I've heard people say the same thing about fireball. Just because it's 3rd level doesn't mean it isn't powerful. 3rd level spells are powerful. I'm playing a 17th level Sorcerer right now and I use more 3rd level spells than any others, just because they are some of the best spells. I have haste, and it hasn't caused many problems. Believe me, the new 3rd edition haste is very well balanced with other spells of its level. There is no need to do anything else to it, but if you feel you must do something, being fatigued afterwards (like Barbarian Rage) is probably a fair compromise.
And forgive me, but the whole aging thing is one thing I was very glad to see go in 3rd edition, it is stupid, senseless and unfair. The idea that casting such a minor spell should permanently damage my character is ludicrous. And yes it does permanently damage your character. Those who said it doesn't really matter are wrong. When you are human, it most certainly does matter. The more powerful spells now cost experience points, which is much better. It reflects the fact that such power should be earned. And unlike years on your life, exp points can be regained. But no, before you ask, I DO NOT THINK HASTE SHOULD COST EXP. It just isn't that good of a spell.