I don't really believe this -- there's too much I don't have a good fit for -- but could you possibly be
Google?
Known for being worth more than three cats,
Absolutely no idea, though Google (now Alphabet) is worth an awful lot. Maybe there's some famously valuable company with a catty name that's out-capitalized 3x by Google, or something.
though my true beginning lies in seeking greater power.
"Google" is a misspelling (accidental at first but deliberately embraced, I think) of "googol", a number equal to $10^{100}$, a large power of 10.
Contrary to popular belief I never needed to begin.
Numbers, unlike material things like people and galaxies, are timeless. (But this doesn't quite work: perhaps a googol is timeless, but Google isn't the same thing.)
On the front page you may get a sizzler,
The front page of Google's search results often has something striking or witty commemorating a particular occasion or person.
but seek me with your voice to receive free queries
If you have an Android phone you can say "OK, Google" to it followed by asking it to do things -- including, e.g., search-engine queries.