as far as swapping it over to a full sportsline, i wouldnt bother. i don't think it would be worth what your putting into it to do the conversion. however changing select things to improve the cars performance isnt a bad idea. im not sure about your car, but i know some of the ecos had the mono shock in the front and non adjustable upper control arms, changing those over to sportsline wouldnt be a bad idea. not sure on the motor, but if you have a solo thats getting tired going to a zenoah would wake it up.
select things are the best way to get some more life out of it. if you want a sportsline, sell what you have and buy a new sportsline. nothing like a new car.