Preamps waste of money?

Depends on the system. Sometimes a passive volume control works and sometimes you need a preamp. I am currently using a placette passive volume control in front of a musical fidelity A3cr amplifier and getting stunning results. However, I have tried the placette with other amps and gotten different results. I will say that when it does work it is the most transparent option. The placette uses stepped vishay resistors.

I too like preamps and find that they can provide an optimal source impedance and gain stage that enhances the sonic performance. Passive is not always "better."

My experience with preamps is that at a certain price point an active preamp can get you the level of detail that a passive provides. In my experience, a passive preamp while giving gobs of details also tends to limit dynamics and drive. The "oomph" as you will. This will be more or less important according to both your music preferences and what matters most to you for musical reproduction. At lower price points this trade-off between detail and drive is a decision that each of us must make for ourselves.

And it must also be noted that passives and attenuators will not work well in a number of situations, particularly when a source has a high output impedance and an amp has a low input impedance.

Others more knowledgeable than myself will likely chime in to add to this.

In my system a good active preamp has made a world of difference. Does the preamp color the sound. Yep. However, the older I get the less I'm concerned about such issues as long as my ears are happy. I've gone the passive route but never found them as beneficial. Whatever works for you.

If your source and amp are a good match, a passive attenuator will work great. If not, a preamp is the correct way to go.
I have a Lightspeed attenuator in my system and love it.