I put a 12 gallon Techron booster in twice annually. Additionally my indy shop includes a cleaning agent (I forget the name of it, but it is was described to me as a much more concentrated version of Techron) with major and minor services (15k and 30k intervals) to deal with hydrocarbon buildup.
I don't know when you should bother with something like seafoaming.
Old Hippie Young Heart
2000 S/3.2 Liter/Tiptronic/Boxster S Sport Package/Cruise Control/Slate Grey Metallic
Red Special Leather Interior/Red Floor Mats/Red Hand Painted Instrument Dials/Roll Bar/Windstop
Small Carbon Package/Leather Wrap Carbon Wheel/Center Console Exterior Color/Alum Carbon Shift Knob
AM/FM Radio w/CD Player & Changer/Digital Sound Package/18" Turbo Wheels/Wheel Caps w/Colored Crest