I've ran into the same issues before and when I do I just take some time off , usually about a week or so and if I get the itch I typically just chip a little and practice putting. Kind of seems like you are becoming more focused on just lowering your handicap than enjoying playing golf, it's definitely great to want to improve but you can't lose track of the big picture which is playing golf for enjoyment.
Well you know what they say....a bad day golfing is better than a good day of work... I get what you are saying and there is some underlying pressure to meet your goals for the game before the courses get covered in leaves, greens punched, lack of daylight.... etc. It is hard to explain but it is a double edged sword. I think I want to back off but then again maybe I don't. Maybe I will declare my rounds practice rounds for a while.
It has been years since I played enough, or put enough pressure on me, to reach the worn out stage. Usually I would hang them up for a while, however, due to your upcoming weather changes, that may no be what you really want to do.
I am not sure of the handicap rules, so I don't know if you can just throw out a series of rounds if just want to go have fun. Since handicap seems to be driving a lot of this, you probably need to figure if you can just throw out the next 2-3 weeks as practice(?).
You can always get a little inventive with your bag to change things up, say play a 7 club bag. Figure out the mix for the course and then improvise as you go.
You may want to pull out some older or vintage clubs and have a go at them. Probably too late to put together a true vintage bag, but since this may be recurring again at some point, spend the winter finding old blades and persimmons and put a set together. Playing with them may be refreshing, or frustrating, who knows, but it will be different.
You can always play some rounds with high handicap golfers to make you feel better about your game. Not sure how well this will work, but it may change your perspective when someone is thrilled with getting a bogey.
If putting is an issue you can try two putters in the bag. I have a couple of putters and I have brought two more than a few times. I have one that is great for slow greens and one that is great for fast greens and one that is good on almost anything... so sometimes I bring both the great ones instead of the good one.
Yes the center of gravity is a little lower compared to the MP-4's and the topline is a little thicker to "hide" the thicker muscle. They are basically between a Mizuno classic blade and a player's cavity back (MP-64). Shape of the muscle and channeling can make a difference but overall performance is going to be similar. If you want a blade looking iron with forgiveness the i blades are the best way to go. Blades will never be obsolete because good players like playing them and they look cool. You'll probably see more "tech blades" like the PXG and Titleist T-MB irons.