If your ETX is a 125, then a 150mm scope will show a noticeable improvement, and a 300mm scope will 'blow your mind'
My first view through an 18incher changed my perspective forever on what I expected a scope to deliver for me.
Aperture fever can be very expensive, but moving from an etx to say, a 10 or 12inch dob could satiate that and leave you with money in your pocket considering the premium you are paying for tracking and portability with an etx.