2000 Chevy Blazer cold air intake and throttle plate spacer

L have a 2000 blazer with a 4.3 liter engnie it has 168850 Kms. The vechile is a gas guzzler l was looking in installing a K&N cold air intake system to improve my gas mileage l was also told to maybe try a throttle plate spacer it is the cheaper way to go. Can l try the throttle plate first and see what differnce it makes first then later install the cold air intake after or am l wasting my money installing both systems? My main concern is improving my gas mileage more so than the performance the better perfofmance is nice too. I would like to know what you think?