This topic comes up every so often:
http://986forum.com/forums/general-discussions/65450-base-vs-s-weight.html
http://986forum.com/forums/general-discussions/59437-base-s-model.html
http://986forum.com/forums/general-discussions/52676-base-vs-s.html
You mention suspension as an upgraded feature of the S, but I don't think that's true. It may be slightly differently tuned to work better with the added power (and rear axle weight) of the S, and/or presence of lack of a tiptronic, (these options all significantly affect rear axle weight). For either base or "S" model Boxter,
M030 is the option you'll want for the upgraded/sportier suspension.