Would it be a waste if I didn't have the whole kit, but just the muffler and tip part? Thx.

 

You mean a muffler welded onto your stock crush-bent piping? It depends on the goal you're after, but I would consider it a waste. If your goal is to have something shiny that makes more noise, then you'd probably be satisfied. Actual performance gains, if any, will be negligible.