I can't keep away from this thread... mainly because I played a Gibson EB0 - the original version of your Epiphone for over 15 years and when I've sought advice about short scale basses got very few replies.
There's nothing wrong with what you've got, it's actually a pretty good EB0 copy: listen to 'sunshine of your love" by Cream, easy bass line to learn, but it's the big fat fuzzy sound which your bass is designed to make with the right amplification - and Jack Bruces fingers !
The Fender Mustang would give you a much cleaner more defined sound. The Warwicks, say a Corvette (if you don't like neck dive don't get a Thumb) are very hi-fi basses so they'd also give you a very well defined sound from a short scale as well as "growl". A Corvette would be around £600 depending on what options you wanted.
How much money do you have ? Alembic have always done short scale necks, they were good enough for Stanley Clarke, but are big money. A Squire Bronco is actually a copy of the old Fender Mustang for little more than £100, it won't compare in sound to the Fender (cheap wood, not string through), but would probably be less muddy than the Epiphone, no neck dive and the money you save would pay for a new bridge, pick ups, tuners and a set up !
Danelectro are another vintage manufacturer of short scale basses, many like them though I've never tried one.
If you've got the cash I'd recommend a Warwick Corvette with a 30 or 32" scale neck for a good all round rock sound and short scale.
chris.