Besides the fact that 'i frutti' can assume a metaphoric meaning which 'la frutta' does not have, is there any other difference between these two wordings?
Yes. Besides the metaphoric meaning you already mentioned (that is widely used), in gereral frutta refers to a type of food, whereas frutti indicates multiple pieces of fruit grouped according to some criterion, usually the fact that they come from a given plant. For instance, you say i frutti di quell'albero sono molto dolci ("the fruits of that tree are very sweat"), and la frutta è un alimento sano ("fruit is healthy"). As usual, handle with care: you may be tempted to say porta i frutti to mean "bring the fruit", but you should use frutta instead. There are grey areas: i frutti più buoni sono quelli appena colti and la frutta più buona è quella appena colta sound both fine to me, but YMMV and regionalisms may kick in of course.