Any carbine that might me used for self defense should have a good pair of irons, and one should practice with them form time to time to keep proficiency up. Just because you primarily run a red dot or scope, doesn't mean that it won't fail on you when you need it most, then the iron sights might save the day.
My eyes aren't that good anymore either, up close anyway.
If you are going to always from a bench at the range, and see how small a group you can shoot, scopes and aftermarket barrels will help, but a Mini isn't the best platform anyway for precision shooting. The Mini is best kept as a light, handy weapon for close to medium range encounters with multiple, larger targets.
I scope a Mini when I first get it to determine what the most accurate load for it is, then remove the scope and put on a red dot.
I'm not going to win any benchrest competitions using my red dot, but man oh man is it quick for hitting randomly spaced silhouette targets as quick as you can pull the trigger. And the dot is great for picking up a target fast in low light, a scope or irons not so much.
By keeping the dot centered inside a bullseye ( or chest on a man sized target ), I can do quite well at ranges up to 300 yards with my Mini-30's, about as far as I want to shoot with that caliber.
I think everyone, at least at first, envisions doing a lot of long range shooting with their Mini's, but it just doesn't work out that way most of the time. Where I live, there are a lot of wide open spaces, but if I want to shoot at something a long ways off, a bolt gun shooting a .308 at minimum, works a lot better.
I have found that a micro red dot like the Burris FastFire or Trijicon RMR to be ideal for a Mini.
Since you have an older "pencil" barrel 187, the fixes you've already done and the ones suggested by RJF, Misfire and others will help a bunch.
Something else that will help, it helped on my 195 Mini-14 almost as much as a strut, is to chop an inch or two off your barrel and do a re-crown. A shorter barrel makes for a stiffer barrel, and most of the factory barrel crowns coming out of the Ruger plant haven't been that great.
Tech rear sights on my Mini's, and the Burris FastFire dot on them:
