First, very good post mate, I agree with your ideas on how to make the game longer but still enjoyable.
To be honest I`m on the edge of giving up too despite playing way too much (real life needs attention too hehe). Simple reason is I dont feel the game "respects" my time and effort. I put helluva of energy, research and time to get best results and get myself some hi end gear. Problem is - for what? I still get 200g Perch on my 60 silver wobler with 4/0 hook. Every big fish that happens to spawn chew off the leader and when I put steel one it gets away haha. I can only speak for myself here but I have a suspicion this is the reason why old time players are giving up as well. There need to be some reward/feeling of accomplishment at the end of the road/grind (call it as you prefer). We have to remember that at the end of the day its still a game and game needs to reward players somehow. If players time and effort vs reward is out of balance, its the quick way to loosing the faithful player base.
Ok, got this off my chest, now lets enjoy whats best in RF4 as the game can still deliver some great moment!