I always sweat the veg, it does make a difference, otherwise the slow cooker just makes it a bit hot and stringy.
you can get away without browning the meat, but I only do that for stuff with plenty of seasoning and a good stock.
Dump bags are a really good concept....I spent a couple of hours chopping/sweating onions and celery before letting it cool and then setting up freezer bags with a variety of meat to have a freezer full of stuff to defrost and hurl into the SC
things like Spanish chicken...onion stuff (as above), add in the sliced chicken, S&P, crushed garlic, paprika, chorizo, great big dod of red pesto make a note on the bag to add drained tinned beans, stock and a tin of tomatoes as you hurl it all into the slow cooker
country chicken....bacon, mustard, leeks, chicken, onion mix
....sky is the limit really!!