Does Global Entry give you any benefits when flying GA?
CBP has a lot of programs. Government programs are confusing. Regarding the two you mention...

Global Entry basically expedites the Customs process for pre-approved travelers, making use of an automated kiosk. The service is available at approved locations, generally major aiports. ClearlyNormally, this program is meant for the commercial traveler. However, large international GA destinations can have this service as well. Example: FLL, one of the nation's busiest international GA airports. They have a global entry kiosk at their GA facility. 

Preclearance means that traveler processing/aircraft inspection are handled before the flight, rather than upon arrival in the US. But, this isn't very widespread yet. Private aircraft preclearance processing is only available at Shannon, Ireland and Oranjestad, Aruba. And the list of airports you can fly to, from what I have seen, is smaller than the list of Ports of Entry.

So no, neither of these programs really helps you out as a Canada/US travelling GA pilot. They aren't for small airports. You have to deal with Customs, APIS, and Ports of Entry, and everything else :)