I would definitely just trade the 328 for a 335. I think you will be much happier in the gains, and nothing you do to the 328 will bring it close to the performance level of a 335. Plus its basically the same car otherwise so you don't have to have the 328 as a back-up. since the only variable on the 335 breaking is the turbos/ waste gate and thats covered.
Plus if you put down 5k and make good payments you'll own the 335 shortly. Also regardless of the mods you make, having any performance mods is going to limit your buyers when you go to sell.