Bottom paint removal/performance

Keep it, as long as the paint is clean it can be pretty rough without problems on boats of this kind.

I doubt that you would ever notice any performance gains. As long as the new paint is sticking and no blisters are cropping up I wouldn't take it down to the gel coat. Is the yard sanding the bottom or just pressure washing and painting? Blasting with a fine media and water is the quickest way to remove the old paint if it's allowed in your area.

With a crazy whim of imagination, I've always thought of my boats bottom like the surface of a golf ball; Those little (some not so little) dimples help it go faster.
I'm sure I'm wrong BUT, Those dimples do make the golf ball go faster / further.

After one heck of a pressure wash, We scuff and feather down any big edges on our ablative bottom. Wash, dry and roll on 8 more gallons every 3 to 4 years.

Our diver always wipes the silt off every mount or so.

Northern boats that spend half of the time on da hill may need a thin coat and a diver OR LOTS of boat activity during the summer

I spent many years in the performance industry & offshore racing. I guarantee you that people spend tens of thousands of dollars to try & gain 1 mph in the racing world. On a sport fish, growth is your enemy. Chips and faded paint aren't going to slow the boat at all. If you had the bottom "blueprinted", I bet you would spend $15-$20k & you MIGHT, might gain a knot at best.
rcrapps, don't laugh, the "golf ball" theory has been tried, tested and tried again but hasn't been successful. The problem is that a golf ball is spinning faster than it's traveling.
Some people think that waxing a bottom will make a boat more slippery but in fact, wax slows a boat down (on a bare hull). a proven fact is that wet sanding with 1200 grit paper makes more speed. Race boats both power and said wet sand. Not practical if your boat sits in the water though.

Years ago when I could afford to go fast, I always pointed to the water with just a lil dimple on it from some light breeze. Figured it trapped mini air bubbled under the hull, It may not have gained much speed but felt like it. That's what gave me the golf ball idea.
Well, I don't go fast any more (-$s) but still enjoy a clean bottom and don't mind any dimples in the paint.

Back to the OP, were carried aweigh on some things but I think we agree; little imperfections in the paint is not going to hurt anything as long as the paint does not peel off at warp speed.

If the bottom paint gets to a certain thickness it will start peeling off in big size chips here and there (palm sized). I had a few yachts soda blasted and started fresh, both picked up right at about 2 knots of speed at cruise and top end. One was a 1999 in 2006, another was a 2007 done last year due to peeling issues (barrier coat and bottom paint lifting). I don't think it's due to the bottom being much smoother, but losing all that weight of each layer of bottom paint.....each gallon of bottom paint on the bottom probably adds at least 20lbs dry, multiply all of those cans for each coat, by every time it gets painted and you could add a few thousand pounds to the boats total weight.