I've played for what seems to be centuries, and I fall into the same hole as what you describe. You practice for endless hours yet your ear doesnt seem to catch the subtle improvements your'e actually making.

Try this as a test...set your guitars down for a couple of days and then go back to them and play. I think you'll be amazed at what you hear. You'll actually hear the improvements and then you'll know you've made progress. Its all very encouraging...