mr. lap - if you tour through the air website, they have the rear flares:
American International Racing
and the front flares:
American International Racing
Jacemond also make a nice widebody kit:
http://www.jacquemond.com/gt27.jpg
rockers there are many, but the gemballa captures the ruf rk, which does the 904 thing quite well:
Gemballa Porsche Boxster s GT New Side Skirts with Air Intake 50 Discount | eBay
http://www.cartype.com/pics/3634/full/ruf_rk_cayman_rs1.jpg
http://www.ultimatecarpage.com/images/large/2865/RUF-RK-Spyder_1.jpg
many choices for tasteful front bumper upgrade. roofs, however, are limited. i'm a fan of the zeintop, but the dmoris unit is nice also. I wish someone would make a top that replaced the tonneau to give the car a fastback appearance, but kept the rear trunk in place (the dmoris almost does this, but it sits on top of the tonneau and looks a bit tacked on as a result):
http://www.9legend.fr/upload/117/600/1/3/2048.jpg
beware your targa idea, as you might start heading in boxster Carrera gt kit car territory:
http://www.evocars-magazin.de/wp-content/gallery/porsche-boxster-carrera-gt-verkauf-2012/porsche-boxster-carrera-gt-mobile-2012-7.jpg