I think there was an assumption of the current glass being a spotting scope , some of which come with interchangeable eyepieces.

24x is more than enough magnification to see mirage , the biggest thing to do to not focus on the target but at intermediate distance . Heat and humidity are huge factors contributing to seeing mirage and a cool dry day the mirage is going to be way harder to see .

And for your original question save your money 200 $ on a spotting scope is not going to be worth it . Spotters are actually all about glass quality unlike a rifle scope and 200 $ spotters have crap glass that will not be up to the same standard as your rifle scope .