Personally, I use my 5C collets for everything I can, for pretty much all of the reasons stated above. A good system with a good collet set isn't cheap, so as a hobbiest, I'm not sure I'd put out the money unless I had a really good reason. When I bought my lathe it came with a nice Royal collet closer system, I just had to buy the collets. As for using a collet block in a 4-jaw chuck, I think you'd be losing most of the advantages of the collet system.
Just my .02 cents.
Ted