SR300 are great basses.
I reckon your best bet would be to Invest in a good set up and try some new strings on your Ibanez.
I had a very early 2000's Ibanez SR500 and it was fantastically sensitive to the strings I put on it. Feeling and sounding awful with nickel 45-105s, bland with stainless Elites 40-100, better with stainless elites 35-95 and absolutely incredible with Thomastik jazz flats.
£300 would get you something different, but not necessarily "better".
If your heart is set on a new bass Second hand would definitely be the way to go, but sadly options will be limited at shops and trade in on your bass wouldn't be a huge sum.