The only real negative effect would be the inability to cary more than one passanger. Other than that it should lighten you car maybe 40 -50 lbs. Also you may get a little more noise in the cabin since the seat isn't there deadning the sound it used to.
May as well try it: as long as you keep it around for a while in case you want to put it back.
I can't realy think of any considerable weight removal options that won't either make the drive less comfortable, cost money to replace parts with lighter ones, or remove functionality from the car.
MY CAR is not even close to being finished but here is the plan: Remove AC: loose weights/less drag on engine,
Manual steering: dito
It will be carburated: it may have a few less pounds in equipment.
Rear seat delete kit: loss of probably 20+n pounds.
I am loosing weight with my setup but also functionality so it's a big trade off.
good luck and keep posting
Weight reduction: Will removing my rear seats help? 
