I find it hard to generalize about t9s. They are all over the place for me. There are some, like Bio's Parasitic Aura and Regen's Moment of Glory, that I consider bread and butter powers that I use frequently. The fact that they're t9 powers doesn't really figure into that. Regen's t9 is a go to if you have to take a tough alpha. Bio's is mostly a buff and debuff you can use.
The ones that have mild crashes, like in Willpower and Shields, also have rather long or unbuffable recharges and get reserved for that special hell for powers that have extremely long recharges. That is, they're 'saved for emergencies' or 'saved for the right occasion' that, when that time comes come, you are so used to ignoring them that you have forgotten what the icon looks like or where you put it. So they don't get used then, either.
Then there are the suicide buttons. These get skipped. Invulnerability's Unstoppable is the prototype. Apparently the one in Energy Aura is similar. I just got my Energy brute to 38 and happily passed it by. Then I started second guessing myself, since Energy Aura seems quite bad out of the box, a weaker version of Invulnerability without the scaling mechanism where more mobs make the armor stronger. I also skipped Energy Cloak, and maybe I need it, but a stealth power on a set with a taunt aura in its mez protection seems full of fail as well. The self-rez buttons ae also usually ignored; why spend a power pick on something you could have in an inspiration? Or a P2W boughten power?