well they're on the same platform, but the evo has about 200 extra stitch welds along the chassis/frame. you also bought this used, could've got an evo used for around 25k i'm betting (if not cheaper) but if you enjoy it, thats all that matters.
if it was me, i'd quit doing performance upgrades and focus on audio, etc. the money that you're putting into the vehicle right now, you're likely to never get back. however if you're getting audio, atleast you can physically take it out of the vehcile and put it in another if and when you decide to get a new vehicle someday.