Should I replace all the copper pipe in my heating system with PEX?
How often does your heating system spring a leak? It's not particularly often in my (long) experience with closed-crcuit hot water heating systems - less than once per 20 years, I'd say, and usually with some outside cause. In general, it is a waste of money to remove/replace a system that's working. To address one of your "benefits" - where do you suppose the heat "lost" from your copper heating pipes goes? Unless the pipes are running on the outside of your house (which would be a bit unusual) it goes to heating your house. Absolutely nothing is gained by "saving" that (small amount of) heat "for the radiators." If the pipes are running outside the building, they should be insulated regardless of their material.

Quick connects are more likely to INCREASE the number of leaks you have over time .vs. leaving the copper pipes alone. Replacing a reliable soldered joint with a complex mechanical seal is not a direction that will benefit your leak statistics. Most people simply work around baseboard heat when redoing walls, floors, etc. and manage to get by just fine without "popping them out." 

You need to use an oxygen barrier type PEX if your heating system is (as is typically the case) a closed circuit system. Copper pipes do that by default. 

You may, or course, do what you like, but this appears to be a somewhat absurd project. There are good arguments for building a NEW system with PEX "in 2014" but really no good reason to rip out a copper system and replace it with PEX and copper.